OFFSET
1,2
COMMENTS
This sequence is infinite since A051179(n) is a term. - Jinyuan Wang, Mar 13 2020
LINKS
Jinyuan Wang, Table of n, a(n) for n = 1..10000
Florian Luca, Positive integers n such that n| a^sigma(n) - 1, Novi Sad Journal of Mathematics, Vol 33, No. 2 (2003), pp. 49-66.
EXAMPLE
2^sigma(15) = 2^24 = 16777216 is congruent to 1 (mod 15), so 15 is a term of the sequence.
MATHEMATICA
l = {1};
For[i = 1, i <= 10^4, i++,
If[Mod[2^DivisorSigma[1, i], i] == 1, l = Append[l, i]]];
l
PROG
(PARI) s=[1]; for(n=1, 10000, if(2^sigma(n)%n==1, s=concat(s, n))); s \\ Colin Barker, Jan 30 2014
(PARI) isok(n) = Mod(2, n)^sigma(n)==1; \\ Altug Alkan, Sep 19 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Joseph L. Pe, Jan 30 2014
EXTENSIONS
a(1) = 1 added by Amiram Eldar, Sep 19 2017
STATUS
approved