OFFSET
1,12
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
EXAMPLE
a(12)=6; the 6 sets are: {3,4}, {4,6}, {2,3,4}, {2,4,6}, {3,4,6}, {2,3,4,6}.
MATHEMATICA
a076078[n_] := Module[{d, i}, d=Divisors[n]; Sum[MoebiusMu[n/d[[i]]]*(2^DivisorSigma[0, d[[i]]]-1), {i, 1, Length[d]}]]; a[n_] := a076078[n]/2-2^(DivisorSigma[0, n]-2)
PROG
(PARI)
A076078(n) = { local(f, l, s, t, q); f = factor(n); l = matsize(f)[1]; s = 0; forvec(v = vector(l, i, [0, 1]), q = sum(i = 1, l, v[i]); t = (-1)^(l - q)*2^prod(i = 1, l, f[i, 2] + v[i]); s += t); s; } \\ This function from David Wasserman
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy and Dean Hickerson, Oct 09 2002
STATUS
approved