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Given an integer  with  distinct prime factors  (where  is number of distinct prime factors function), if the equality
holds true, then  is a primary pseudoperfect number. Equivalently,
if  is a primary pseudoperfect number.
The first few primary pseudoperfect numbers are 2, 6, 42, 1806, 47058, 2214502422, 52495396602, 8490421583559688410706771261086, the first four of these being each one less than the first four terms of Sylvester's sequence; these are listed in A054377 of Sloane's OEIS. Presently it's not known whether there are any odd primary pseudoperfect numbers.
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