OFFSET
1,1
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
usigma[n_] := Block[{d = Divisors[n]}, Plus @@ Select[d, GCD[ #, n/# ] == 1 &]]; Complement[ Range[1017], Table[3k - 2, {k, 340}], (Select[ Range[220000], DivisorSigma[1, # ] == 2usigma[ # ] &] - 108)/216] (* Robert G. Wilson v, Aug 28 2004 *)
PROG
(PARI) is(k) = if(k % 3 == 1, 0, my(f = factor(216*k + 108)); sigma(f) != 2 * prod(i = 1, #f~, 1 + f[i, 1]^f[i, 2])); \\ Amiram Eldar, Aug 31 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Ralf Stephan, Aug 26 2004
STATUS
approved