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 A246540 G.f.: Sum_{n>=0} 4^n * x^n / (1-x)^(2*n+1) * [Sum_{k=0..n} C(n,k)^2 * x^k]^2. 2
 1, 5, 37, 325, 3125, 31925, 339077, 3700645, 41200981, 465736725, 5328229797, 61552244485, 716791570549, 8403794763125, 99096946864325, 1174370518273125, 13977636401394069, 167001257979441365, 2002052157653251557, 24073717683854557125, 290261630170911545525, 3508332484300450371125 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS a(n) == 5 (mod 16) for n>=1. LINKS FORMULA G.f.: Sum_{n>=0} x^n / (1-4*x)^(2*n+1) * [Sum_{k=0..n} C(n,k)^2 * 4^k * x^k]^2. G.f.: Sum_{n>=0} x^n * Sum_{k=0..n} C(n,k)^2 * 4^k * Sum_{j=0..k} C(k,j)^2 * x^j. G.f.: Sum_{n>=0} x^n * Sum_{k=0..n} C(n,k)^2 * 4^(n-k) * Sum_{j=0..k} C(k,j)^2 * 4^j * x^j. a(n) = Sum_{k=0..[n/2]} 4^k * Sum_{j=0..n-2*k} C(n-k, k+j)^2 * C(k+j, j)^2 * 4^j. Recurrence: (n-3)*n^2*a(n) = 5*(n-3)*(3*n^2 - 3*n + 1)*a(n-1) - (n-1)*(23*n^2 - 92*n + 65)*a(n-2) - 5*(n-2)*(15*n^2 - 60*n + 53)*a(n-3) - 4*(n-3)*(23*n^2 - 92*n + 65)*a(n-4) + 80*(n-1)*(3*n^2 - 21*n + 37)*a(n-5) - 64*(n-4)^2*(n-1)*a(n-6). - Vaclav Kotesovec, Nov 05 2014 a(n) ~ ((13+3*sqrt(17))/2)^(n+1) / (8*Pi*n). - Vaclav Kotesovec, Nov 05 2014 EXAMPLE G.f.: A(x) = 1 + 5*x + 37*x^2 + 325*x^3 + 3125*x^4 + 31925*x^5 +... where A(x) = 1/(1-x) + 4*x/(1-x)^3*(1+x)^2 + 4^2*x^2/(1-x)^5*(1 + 2^2*x + x^2)^2 + 4^3*x^3/(1-x)^7*(1 + 3^2*x + 3^2*x^2 + x^3)^2 + 4^4*x^4/(1-x)^9*(1 + 4^2*x + 6^2*x^2 + 4^2*x^3 + x^4)^2 + 4^5*x^5/(1-x)^11*(1 + 5^2*x + 10^2*x^2 + 10^2*x^3 + 5^2*x^4 + x^5)^2 + 4^6*x^6/(1-x)^13*(1 + 6^2*x + 15^2*x^2 + 20^2*x^3 + 15^2*x^4 + 6^2*x^5 + x^6)^2 +... MATHEMATICA Table[Sum[4^k * Sum[Binomial[n-k, k+j]^2 * Binomial[k+j, j]^2 * 4^j, {j, 0, n-2*k}], {k, 0, Floor[n/2]}], {n, 0, 20}] (* Vaclav Kotesovec, Nov 05 2014 *) PROG (PARI) /* By definition: */ {a(n)=local(A=1); A=sum(m=0, n, 4^m*x^m/(1-x)^(2*m+1) * sum(k=0, m, binomial(m, k)^2 * x^k)^2 +x*O(x^n)); polcoeff(A, n)} for(n=0, 25, print1(a(n), ", ")) (PARI) /* By a binomial identity: */ {a(n)=local(A=1); A=sum(m=0, n, x^m/(1-4*x)^(2*m+1) * sum(k=0, m, binomial(m, k)^2 * 4^k * x^k)^2 +x*O(x^n)); polcoeff(A, n)} for(n=0, 25, print1(a(n), ", ")) (PARI) /* By a binomial identity: */ {a(n)=polcoeff(sum(m=0, n, x^m*sum(k=0, m, binomial(m, k)^2 * 4^k * sum(j=0, k, binomial(k, j)^2 * x^j)+x*O(x^n))), n)} for(n=0, 25, print1(a(n), ", ")) (PARI) /* By a binomial identity: */ {a(n)=polcoeff(sum(m=0, n, x^m*sum(k=0, m, binomial(m, k)^2 * 4^(m-k) * sum(j=0, k, binomial(k, j)^2 * 4^j * x^j)+x*O(x^n))), n)} for(n=0, 25, print1(a(n), ", ")) (PARI) /* By a formula for a(n): */ {a(n)=sum(k=0, n\2, sum(j=0, n-2*k, 4^k * binomial(n-k, k+j)^2 * binomial(k+j, j)^2 * 4^j))} for(n=0, 25, print1(a(n), ", ")) CROSSREFS Cf. A246538, A246539, A246056, A246423, A243948, A245929, A227845, A245925. Sequence in context: A176818 A068785 A199562 * A177395 A258296 A197713 Adjacent sequences:  A246537 A246538 A246539 * A246541 A246542 A246543 KEYWORD nonn AUTHOR Paul D. Hanna, Aug 28 2014 STATUS approved

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Last modified June 17 07:00 EDT 2019. Contains 324183 sequences. (Running on oeis4.)