login
A078549
Non-balanced numbers in A015771.
6
749, 1498, 2247, 2568, 2889, 2996, 3745, 3959, 4494, 5778, 5992, 6741, 7490, 7918, 8876, 8988, 9416, 9737, 9994, 11235, 11556, 11877, 11984, 12733, 13482, 14231, 14445, 14980, 16264, 17976, 18404, 19474, 20223, 20804, 22363, 22470, 23112
OFFSET
1,1
LINKS
FORMULA
sigma_13(a(n)) mod phi(a(n)) = 0; sigma(a(n)) mod phi(a(n)) <> 0.
MATHEMATICA
q[n_] := Sign[Mod[DivisorSigma[{1, 13}, n], EulerPhi[n]]] == {1, 0}; Select[Range[24000], q] (* Amiram Eldar, Apr 11 2024 *)
PROG
(PARI) is(n) = {my(f = factor(n), phi = eulerphi(f)); (sigma(f) % phi) && !(sigma(f, 13) % phi); } \\ Amiram Eldar, Apr 11 2024
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 05 2002
STATUS
approved