OFFSET
1,2
COMMENTS
Perfect powers: 1, 27, 1331, 6859, 79507, 205379, 300763, 571787, 1225043, 2248091, 2685619, 4330747, 5735339, 9393931, ...
EXAMPLE
14 is in this sequence because it has 4 divisors (1, 2, 7, 14) and 1 + 2 + 7 + 14 = 24 also has 4 power-of-two-divisors 1, 2, 4, 8.
MATHEMATICA
Select[Range[323], DivisorSigma[0, #] == 1 + IntegerExponent[ DivisorSigma[1, #], 2] &] (* Giovanni Resta, Sep 19 2019 *)
PROG
(Magma) [n: n in [1..300] | NumberOfDivisors(n) eq Valuation(2*SumOfDivisors(n), 2)];
(PARI) isA309621(n) = (numdiv(n)==(1+valuation(sigma(n), 2))); \\ Antti Karttunen, Aug 12 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Juri-Stepan Gerasimov, Aug 10 2019
STATUS
approved