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 A202831 E.g.f.: exp(4*x/(1-5*x)) / sqrt(1-25*x^2). 9
 1, 4, 81, 1444, 44521, 1397124, 58354321, 2574344644, 136043683281, 7657406908804, 489836445798001, 33351743794661604, 2504378700538997881, 199445618093659242244, 17189578072429077875121, 1564487078400498014277124, 152146464623361858013314721 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 FORMULA a(n) = A202832(n)^2, where the e.g.f. of A202832 is exp(2*x + 5*x^2/2). a(n) = ( Sum_{k=0..[n/2]} 2^(n-3*k)*5^k * n!/((n-2*k)!*k!) )^2. a(n) ~ n^n*exp(4*sqrt(n/5)-2/5-n)*5^n/2. - Vaclav Kotesovec, May 23 2013 D-finite with recurrence: a(n) = (5*n-1)*a(n-1) + 5*(n-1)*(5*n-1)*a(n-2) - 125*(n-1)*(n-2)^2*a(n-3). - Vaclav Kotesovec, May 23 2013 EXAMPLE E.g.f.: 1 + 4*x + 81*x^2/2! + 1444*x^3/3! + 44521*x^4/4! + 1397124*x^5/5! +... where A(x) = 1 + 2^2*x + 9^2*x^2/2! + 38^2*x^3/3! + 211^2*x^4/4! + 1182^2*x^5/5! +...+ A202832(n)^2*x^n/n! +... MATHEMATICA CoefficientList[Series[Exp[4*x/(1-5*x)]/Sqrt[1-25*x^2], {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, May 23 2013 *) PROG (PARI) {a(n)=n!*polcoeff(exp(4*x/(1-5*x)+x*O(x^n))/sqrt(1-25*x^2+x*O(x^n)), n)} (PARI) {a(n)=n!^2*polcoeff(exp(2*x+5*x^2/2+x*O(x^n)), n)^2} (PARI) {a(n)=sum(k=0, n\2, 2^(n-3*k)*5^k*n!/((n-2*k)!*k!))^2} CROSSREFS Cf. A202832, A202827, A202828, A202829, A202833, A202835, A202836. Sequence in context: A017006 A041189 A123198 * A264197 A221251 A128911 Adjacent sequences:  A202828 A202829 A202830 * A202832 A202833 A202834 KEYWORD nonn AUTHOR Paul D. Hanna, Dec 25 2011 STATUS approved

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Last modified April 5 02:58 EDT 2020. Contains 333238 sequences. (Running on oeis4.)