OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..1000
FORMULA
{n: A084301(n) = 5}. - R. J. Mathar, May 19 2020
EXAMPLE
4th powers of primes of the form 6k+1 are here because sigma[p^4]=p^4+p^3+p^2+p+1 congruent 1+1+1+1+1=5 mod 6. There are also other fourth powers, like 38416=(2*7)^4, 194481=(3*7)^4, 456976=(2*13)^4, and solutions which are not fourth powers like 9604=2^2*7^4 and 21609=3^2*7^4.
MATHEMATICA
Do[s=Mod[DivisorSigma[1, n], 6]; If[s==5, Print[n]], {n, 1, 1000000}]
Select[Range[1600000], Mod[DivisorSigma[1, #], 6]==5&] (* Harvey P. Dale, Jul 06 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Aug 22 2002
STATUS
approved