OFFSET
1,2
COMMENTS
Multiplicative because A000594 is. - Christian G. Bower, May 16 2005
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = Sum_{d|n} tau(d)tau(n/d) where tau(n) = A000594(n) is Ramanujan's tau function.
EXAMPLE
G.f. = x - 48*x^2 + 504*x^3 - 2368*x^4 + 9660*x^5 - 24192*x^6 - 33488*x^7 + ...
MATHEMATICA
a[n_] := DivisorSum[n, RamanujanTau[#]*RamanujanTau[n/#]&]; Array[a, 30] (* Jean-François Alcover, Nov 14 2015 *)
PROG
(PARI) {a(n) = local(A); if( n<1, 0, A = Vec( eta(x + x^n*O(x))^24); sumdiv(n, d, A[d] * A[n/d]))}; /* Michael Somos, Jul 16 2004 */
(Perl) use ntheory ":all"; for my $n (1..50) { say divisor_sum($n, sub { my $d=shift; ramanujan_tau($d)*ramanujan_tau($n/$d) } # Dana Jacobsen, Sep 05 2015
CROSSREFS
KEYWORD
sign,mult
AUTHOR
STATUS
approved