# self number

An integer $n$ that in a given base $b$ lacks a digitaddition generator.

Consider, for example, the integer 41 in base 10. It can be expressed as 34 + 3 + 4. For 42, however, there is no such digitaddition, hence it is a self number.

If $2|b$, all odd $n will be self numbers.

Though self numbers form a small proportion of most ranges of $2b$ consecutive integers, there are infinitely many of them: The recurrence relation $S_{i}=(b-2)b^{i-1}+S_{i-1}+(b-2)$ (with $S_{1}=b-1$ if $2|b$ and $S_{1}=b-2$ otherwise) will give an incomplete though infinite list of self numbers.

Reference

Kaprekar, D. R. The Mathematics of New Self-Numbers. Devaiali, 1963: 19 - 20

Title self number SelfNumber 2013-03-22 15:56:15 2013-03-22 15:56:15 CompositeFan (12809) CompositeFan (12809) 6 CompositeFan (12809) Definition msc 11A63 Columbian number Colombian number self-number