OFFSET
1,1
COMMENTS
LINKS
Jinyuan Wang, Table of n, a(n) for n = 1..10000
FORMULA
Solutions of k^2 mod sigma(k) = d(k).
EXAMPLE
sigma(8) = 15 and 8^2 mod 15 = 4 = d(8).
MAPLE
with(numtheory): op(select(n->n^2 mod sigma(n)=tau(n), [$1..1214]));
MATHEMATICA
Select[Range[1225], PowerMod[#1, 2, #3] == #2 & @@ Prepend[DivisorSigma[{0, 1}, #], #] &] (* Michael De Vlieger, Jan 18 2019 *)
PROG
(PARI) for(k=1, 2000, x=sigma(k); if(Mod(k, x)^2==Mod(numdiv(k), x), print1(k, ", "))) \\ Jinyuan Wang, Feb 03 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paolo P. Lava, Jan 08 2019
STATUS
approved