OFFSET
1,3
COMMENTS
If p is prime but not a Fermat prime then a(p)=1.
Least k such that a(k) = n: 1, 3, 6, 28, 32, 12, 112, 30, 54, 24, 36, 126, 48, 200, 90, 160, 60, 264, 96, 400, ..., . - Robert G. Wilson v, Aug 07 2008
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 &]]; f[n_] := Block[{c = 0, m = 1}, While[m <= n, If[ Mod[n, usigma@ m] == 0, c++ ]; m++ ]; c]; Array[f, 102] (* Robert G. Wilson v, Aug 07 2008 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Yasutoshi Kohmoto, Aug 01 2008
EXTENSIONS
More terms from Robert G. Wilson v, Aug 07 2008
STATUS
approved