1,2

Table of n, a(n) for n=1..5.

25 is a term because it is an odd number and sigma(25) divides 2^25 - 1.

(PARI) is(n)=Mod(2, sigma(n))^n==1&&n%2==1;

Cf. A000203, A000225, A278836.

Sequence in context: A196520 A228536 A191559 * A237522 A116197 A023924

Adjacent sequences: A279036 A279037 A279038 * A279040 A279041 A279042

nonn,more

Altug Alkan, Dec 04 2016

approved