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 A221535 E.g.f.: Sum_{n>=0} a(n) * (cos(n^2*x) - sin(n^2*x)) * x^n/n!  =  1 + x. 2
 1, 1, 2, 27, 1160, 113385, 21060816, 6623049027, 3256046222848, 2359986757857297, 2411094849547390720, 3350982557290104443883, 6155509617679334624756736, 14592373629282306879174535161, 43755759571493116198207431532544, 163135210694347619479784565520981395 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA a(n) = Sum_{k=1..n-1} (-1)^[(n-k-1)/2] * binomial(n,k) * k^(2*n-2*k) * a(k) for n>1 with a(0)=a(1)=1. EXAMPLE By definition, the coefficients a(n) satisfy: 1+x = 1 + 1*(cos(x)-sin(x))*x + 2*(cos(4*x)-sin(4*x))*x^2/2! + 27*(cos(9*x)-sin(9*x))*x^3/3! + 1160*(cos(16*x)-sin(16*x))*x^4/4! + 113385*(cos(25*x)-sin(25*x))*x^5/5! +...+ a(n)*(cos(n^2*x)-sin(n^2*x))*x^n/n! +... PROG (PARI) a(n)=local(A=[1, 1], N); for(i=1, n, A=concat(A, 0); N=#A; A[N]=(N-1)!*(-Vec(sum(m=0, N-1, A[m+1]*x^m/m!*(cos(m^2*x+x*O(x^N))-sin(m^2*x+x*O(x^N)))))[N])); A[n+1] for(n=0, 25, print1(a(n), ", ")) (PARI) a(n)=if(n<2, 1, sum(k=1, n-1, (-1)^((n-k-1)\2)*a(k)*binomial(n, k)*k^(2*n-2*k))) for(n=0, 25, print1(a(n), ", ")) CROSSREFS Cf. A218798, A195736, A209316, A221534. Sequence in context: A182934 A078102 A221534 * A067075 A015217 A320417 Adjacent sequences:  A221532 A221533 A221534 * A221536 A221537 A221538 KEYWORD nonn AUTHOR Paul D. Hanna, Jan 19 2013 STATUS approved

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Last modified February 25 22:55 EST 2020. Contains 332270 sequences. (Running on oeis4.)