OFFSET
0,4
LINKS
Danny Rorabaugh, Table of n, a(n) for n = 0..1000
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 786
FORMULA
G.f.: (Sum_{j>=i} (A000010(j)/j)*log((x^j-1)/(2*x^j-1)))^2.
MAPLE
pairs spec := [S, {B=Sequence(Z, 1 <= card), C=Cycle(B), S=Prod(C, C)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
h := n -> add(numtheory: phi(j)/j*log((x^j-1)/(2*x^j-1)), j=1..n): seq(coeff(series(h(n)^2, x, n+1), x, n), n=0..34); # Danny Rorabaugh, Oct 25 2015
PROG
(Sage) var('x'); a = lambda n: expand(sum([taylor(euler_phi(i)/i * log((x^i - 1)/(2*x^i - 1)), x, 0, n) for i in range(1, n+1)])^2).coefficient(x^n) # Danny Rorabaugh, Oct 25 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
EXTENSIONS
More terms from Danny Rorabaugh, Oct 25 2015
STATUS
approved