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 A156134 Q_2n(sqrt(2)) (see A104035). 4
 1, 5, 157, 12425, 1836697, 436366445, 152053957237, 73053601590065, 46283414838553777, 37386890114969267285, 37503815980582784378317, 45739346519434253222582105, 66650214918099514832427062857, 114363498315755726948758209518525, 228234739109951323288351261455519397 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS G. C. Greubel, Table of n, a(n) for n = 0..207 FORMULA G.f. cos(x)/(1 - 3*sin(x)^2) = 1 + 5*x^2/2! + 157*x^4/4! + 12425*x^6/6! + ... - Peter Bala, Feb 06 2017 MAPLE with(gfun): series(cos(x)/(1-3*sin(x)^2), x, 30): L := seriestolist(%): seq(op(2*i-1, L)*(2*i-2)!, i = 1..floor((1/2)*nops(L))); # Peter Bala, Feb 06 2017 MATHEMATICA With[{nmax = 50}, CoefficientList[Series[Cos[x]/(1 - 3*Sin[x]^2), {x, 0, nmax}], x]*Range[0, nmax]!][[1 ;; ;; 2]] (* G. C. Greubel, Mar 29 2018 *) PROG (PARI) x='x+O('x^50); v=Vec(serlaplace(cos(x)/(1 - 3*sin(x)^2))); vector(#v\2, n, v[2*n-1]) \\ G. C. Greubel, Mar 29 2018 CROSSREFS Cf. A012494, A001209, A000364, A000281, A002437. Cf. other sequences with a g.f. of the form cos(x)/(1 - k*sin^2(x)): A012494 (k=-1), A001209 (k=1/2), A000364(k=1), A000281 (k=2), A002437 (k=4). Sequence in context: A305087 A316738 A009082 * A183263 A155208 A321529 Adjacent sequences:  A156131 A156132 A156133 * A156135 A156136 A156137 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Nov 06 2009 STATUS approved

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Last modified March 20 05:45 EDT 2019. Contains 321344 sequences. (Running on oeis4.)