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PlanetMath is a virtual community which aims to help make mathematical knowledge more accessible. PlanetMath's content is created collaboratively: the main feature is the mathematics encyclopedia with entries written and reviewed by members. The entries are contributed under the terms of the Creative Commons By/Share-Alike License in order to preserve the rights of authors, readers and other content creators in a sensible way. We use LaTeX, the lingua franca of the worldwide mathematical community. On February 13th 2013, PlanetMath.org was updated to use the new software system Planetary. Some release notes are here. Please report bugs in the Planetary Bugs Forum or on Github.

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[p] Message viewership by akdevaraj Aug 30
I have written many messages (posts ). However I do not know how many read my messages. Perhaps rspuzio will consider setting up software to enable viewership.

[p] Fermat's theorem in k(i) (c0ntd) by akdevaraj Aug 28
When we carry out the following operations we get a quotient which is a Gaussian integer: a)((21+i)^20-1)/21 b)((21+i)^(21-i)-1)/21 c)((21+i)^(21-i)-i/21 and d)((341+i)^340-1)/341 Note that a) 341 is also a pseudoprime in k(1) and b) i is also one of the unities in k(i).

Search not working. How can I find an item? by jaimeglz Aug 25
Dear planetmath.org: It has been several months since I have been able to perform a successful search at your site. The fact that I have not been able to find articles either by searching, nor by MSC has rendered (at least for me) planetmath.org practically unusable. In your home page, I see that new articles are being contributed regularly. This makes me wonder: Is there a way to sidestep the search problem? Is there am alternative way to get to an article (say, "Pascal's formula", or "Pascal's rule")? Is there an alternative way of reaching articles under MSC 05A10? Thanks in advance.>

[p] Egyptian Middle Kingdom arithmetic progressions by milogardner Aug 22
In 1987, Egyptologist Gay Robins, and Charles Shute, wrote a book on the Rhind Mathematical Papyrus (RMP). Five years later Egyptologist John Legon wrote on the KP and the same class of arithmetic proportions used in the RMP. The KP and RMP report the same arithmetic proportion method to find the largest term. The method: take 1/2 of the difference, 1/2 of 5/6 (5/12 in the KP) times the number of differences (nine times 5/12 = 15/4 in the KP) plus the sum of the A.P progression (100 in the KP) divided by the number of terms (10 meant 100/10 = 10 in the KP). Finally add column 11’s result, 3 3/4, to 10, and the largest term, 13 3/4. In unit fractions, the context of the text, add column 11: 5/12 times 9 writing 3 3/4 as 3 2/3 1/12 to 10 in column 12 beginning with the largest term 13 2/3 1/12. The scribe subtracted 5/6 nine times created remaining terms of the arithmetic progression. Robins-Shute confused aspects of the problem by omitting the sum divided by the number of terms, a topic cited in a closely related RMP 40 problem. A scribal algebraic statement matched pairs added to 20 reporting five pairs summed to 100, a set of facts included in RMP 40. The complete KP method found the largest term facts reported in RMP 64 and RMP 40 by John Legon in 1992. Scholars have parsed Rhind Mathematical Papyrus 40 a problem that asked that 100 loaves of bread to be shared between five men by finding the smallest term of an arithmetic progression. C. A confirmation of the Kahun Papyrus arithmetic progression method must include discussions of RMP 40 and RMP 64. In RMP 64 Ahmes asked 10 men to share 10 hekats of barley with a differential of 1/8 defining an arithmetical progression. Robins and Shute reported: ”the scribe knew the rule that, to find the largest term of the arithmetical progression, he must add half the difference to the average number of terms as many times as there are common differences, that is, one less than the number of terms”. 1. number of terms: 10 2. arithmetical progression difference: 1/8 3. arithmetic progression sum: 10 The scribe used the following facts to find the largest term. 1. one-half of differences, 1/16, times number of terms minus one, 9, 1/16 times 9 = 9/16 2. The computed parameter(1), was found by 10, the sum, divided by 10, the number of terms. It was inserted by Robins-Shute, but had not been high-lighted, citing 1 + 1/2 + 1/16, or 1 9/16, the largest term. The remaining nine terms were found by subtracting 1/8 nine times to obtain the remaining barley shares. That is, the KP scribe used formula 1.0:1111111 (1/2)d(n-1) + S/n = Xn (formula 1.0) with, d = differential, n = number of terms in the series, S = sum of the series, Xn = largest term in the series allowed three(of the four) parameters: d, n, S and Xn, to algebraically find the fourth parameter. When n was odd, x (n/2) = S/n, and x 1 + xn = x2 + x(n -1) = x3 + x(n -2) = … = x(n/2) = S/n, Note that Robins-Shute omitted the sum divided by the number of terms (S/n): A modern footnote cites Carl Friedrich Gauss implementing as a grammar school student a solution to the n = even case. Ahmes and Gauss found the sum for 1 to 100 by using d = 1 following the same rule. Ahmes and Gauss reached the sum 5050 based on 50 pairs of 101 (1 + 101 = 2 + 99 = 3 + 98 = …) by using an identical arithmetic progression rule.

[p] Kahun Papyrus, a 1800 BCE text, and arithmetic progressions by milogardner Aug 22
The KP http://planetmath.org/kahunpapyrusandarithmeticprogressions method was known to Ahmes in 1650 BCE

[p] • gg by Rushike SLR Aug 18
\begin{itemize} \item \end{itemize}\begin{flushleft} \end{flushleft} \textbf{}gg

[p] pseudoprimes in k(i) (contd) by akdevaraj Aug 17
561 is a pseudoprime to any base of shape (11*k+I) where k belongs to N. This is in addition to the other bases indicated in the previous message.

[p] years divisible by 100 by bbmath Aug 14
There is an exception to "years divisible by 4 being leap years": If a year is divisible by 100 (such years are divisible by 4), such a year is a leap year ONLY IF it is also divisible by 400. For example, 2000 was a leap year, but 1900 was not. Shockley's "Introduction to Number Theory" contains a "day of the week" formula that includes the above fact.

[P] Carmichael numbers and Devaraj numbers by akdevaraj Aug 9
Carmichael numbers constitute a sub-set of Devaraj numbers. To understand more about them refer sequences A 104016, A 104017 and A 162290. Some interesting facts pertaining to them will follow.

[P] The entry "division" became invisible. by pahio Aug 8
The reason was a dollar-sign error =o) Corrected! BTW, the PM search engine has long been out of order. It's quite difficult to find entries on a wanted subject.

[P] Pl. see the older entry http: by pahio Aug 7
Pl. see the older entry http://planetmath.org/divisibilitytest

[p] Mangammal primes by akdevaraj Aug 7
Definition: These are the impossible prime factors of 3^n - 2 (n belongs to N). This is identical with the sequence A123239 (OEIS ).

[p] Nice solution by burgess Aug 6
Nice solution

[P] division of two numbers by pahio Aug 4
Please see e.g. the entry http://planetmath.org/division BTW, one cannot write "P(R)*0 = 0" since your P(R) is not a _number_