OFFSET
0,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..1000 (terms 0..60 from N. J. A. Sloane)
Victor S. Miller, Counting Matrices that are Squares, arXiv:1606.09299 [math.GR], 2016.
FORMULA
G.f.: Product_{n>=1} (1-2*z^(2*n))/((1-2*z^n)*(1-2*z^(4*n)). - Jean-François Alcover, Dec 12 2018, after Victor S. Miller.
MAPLE
seq(coeff(series(mul((1-2*x^(2*k))/((1-2*x^k)*(1-2*x^(4*k))), k=1..n), x, n+1), x, n), n = 0 .. 40); # Muniru A Asiru, Dec 13 2018
MATHEMATICA
terms = 40;
Product[(1-2z^(2n))/(1-2z^n)/(1-2z^(4n)), {n, 1, terms}] + O[z]^terms // CoefficientList[#, z]& (* Jean-François Alcover, Dec 12 2018 *)
PROG
(PARI) seq(n)=Vec(prod(i=1, n, (1-2*x^(2*i))/((1-2*x^i)*(1-2*x^(4*i)) + O(x*x^n)))) \\ Andrew Howroyd, Dec 12 2018
(Magma) m:=40; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!( (&*[(1-2*x^(2*k))/((1-2*x^k)*(1-2*x^(4*k))): k in [1..m/2]]))); // G. C. Greubel, Dec 16 2018
(Sage) m=40; s=(prod((1-2*x^(2*k))/((1-2*x^k)*(1-2*x^(4*k))) for k in (1..m/2))).series(x, m); s.coefficients(x, sparse=False) # G. C. Greubel, Dec 16 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jun 25 2016
STATUS
approved