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 A098278 D(n,0)/2^n, where D(n,x) is triangle A098277. 2
 1, 1, 3, 21, 267, 5349, 154923, 6120741, 316271787, 20701782309, 1673934058923, 163850823271461, 19093313058395307, 2611858473935397669, 414452507370456337323, 75508557963926980473381 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Ange Bigeni, Evgeny Feigin, Symmetric Dellac configurations, arXiv:1808.04275 [math.CO], 2018. A. Randrianarivony and J. Zeng, Une famille de polynômes qui interpole plusieurs suites..., Adv. Appl. Math. 17 (1996), 1-26. FORMULA G.f.: Sum_{n>=0} a(n)*x^n = 1/(1-1*1*x/(1-1*2*x/(1-2*3*x/(1-2*4*x/...)))). G.f.: Sum_{n>=0} n!^2 * x^n / Product_{k=1..n} (1 + k*(k+1)/2*x). - Paul D. Hanna, Sep 05 2012 G.f.: 1/G(0) where G(k) = 1 - x*(k+1)*(2*k+1)/(1 - x*(k+1)*(2*k+2)/G(k+1) ); (continued fraction). - Sergei N. Gladkovskii, Jan 14 2013. a(n+1) = Sum_{k, 0<=k<=n} A098277(n,k)*(1/2)^k. - Philippe Deléham, Feb 08 2013 EXAMPLE G.f.: A(x) = 1 + x + 3*x^2 + 21*x^3 + 267*x^4 + 5349*x^5 +... where A(x) = 1 + x/(1+x) + 2!^2*x^2/((1+x)*(1+3*x)) + 3!^2*x^3/((1+x)*(1+3*x)*(1+6*x)) + 4!^2*x^4/((1+x)*(1+3*x)*(1+6*x)*(1+10*x)) +... - Paul D. Hanna, Sep 05 2012 MATHEMATICA d[0, _] = 1; d[n_, x_] := d[n, x] = (x+1)(x+2)d[n-1, x+2]-x(x+1)d[n-1, x]; a[n_] := d[n, 0]/2^n; Table[a[n], {n, 0, 15}] (* Jean-François Alcover, Oct 26 2018 *) PROG (PARI) {a(n)=polcoeff(sum(m=0, n, m!^2*x^m/prod(k=1, m, 1+k*(k+1)/2*x +x*O(x^n))), n)} \\ Paul D. Hanna, Sep 05 2012 CROSSREFS Sequence in context: A012131 A322224 A221094 * A269938 A277454 A215127 Adjacent sequences:  A098275 A098276 A098277 * A098279 A098280 A098281 KEYWORD nonn AUTHOR Ralf Stephan, Sep 07 2004 STATUS approved

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Last modified August 22 00:43 EDT 2019. Contains 326169 sequences. (Running on oeis4.)