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A154895
Perfect numbers whose number of proper divisors is prime.
0
6, 28, 8128, 137438691328, 2305843008139952128
OFFSET
1,1
COMMENTS
The next term is too large to include in the data section. If there are no odd perfect numbers then the next term is a(6) = 2^606 * (2^607 - 1) = 1.410... * 10^365. - Amiram Eldar, Jul 29 2020
FORMULA
a(n) = A006516(A172461(n)), assuming that odd perfect numbers do not exist. - Amiram Eldar, Jul 29 2020
EXAMPLE
28 is member because the number of proper divisors of 28 is 5, a prime number.
MATHEMATICA
Table[2^(p-1)*(2^p-1), {p, Select[MersennePrimeExponent[Range[8]], PrimeQ[2# - 1] &]}] (* Amiram Eldar, Jul 29 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Omar E. Pol, Jan 25 2009
STATUS
approved