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 A226733 G.f.: 1 / (1 + 8*x*G(x)^2 - 10*x*G(x)^3) where G(x) = 1 + x*G(x)^4 is the g.f. of A002293. 4
 1, 2, 18, 142, 1186, 10152, 88414, 779508, 6936066, 62159224, 560238728, 5072970366, 46114086446, 420558296888, 3846232573236, 35261290343112, 323952686556354, 2981787128165592, 27491128592627800, 253835886034173848, 2346892194318851016, 21724880414632781472 (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) = Sum_{k=0..n} C(2*k, n-k) * C(4*n-2*k, k). a(n) = Sum_{k=0..n} C(n+2*k, n-k) * C(3*n-2*k, k). a(n) = Sum_{k=0..n} C(2*n+2*k, n-k) * C(2*n-2*k, k). a(n) = Sum_{k=0..n} C(3*n+2*k, n-k) * C(n-2*k, k). a(n) = Sum_{k=0..n} C(4*n+2*k, n-k) * C(-2*k, k). G.f.: 1 / (1 - 2*x*G(x)^2 - 10*x^2*G(x)^6) where G(x) = 1 + x*G(x)^4 is the g.f. of A002293. a(n) ~ 2^(8*n+3/2)/(3^(3*n+3/2)*sqrt(Pi*n)). - Vaclav Kotesovec, Jun 16 2013 EXAMPLE G.f.: A(x) = 1 + 2*x + 18*x^2 + 142*x^3 + 1186*x^4 + 10152*x^5 +... A related series is G(x) = 1 + x*G(x)^4, where G(x) = 1 + x + 4*x^2 + 22*x^3 + 140*x^4 + 969*x^5 + 7084*x^6 +... G(x)^2 = 1 + 2*x + 9*x^2 + 52*x^3 + 340*x^4 + 2394*x^5 + 17710*x^6 +... G(x)^3 = 1 + 3*x + 15*x^2 + 91*x^3 + 612*x^4 + 4389*x^5 + 32890*x^6 +... such that A(x) = 1/(1 + 8*x*G(x)^2 - 10*x*G(x)^3). MATHEMATICA Table[Sum[Binomial[2*n+2*k, n-k]*Binomial[2*n-2*k, k], {k, 0, n}], {n, 0, 20}] (* Vaclav Kotesovec, Jun 16 2013 *) PROG (PARI) {a(n)=local(G=1+x); for(i=0, n, G=1+x*G^4+x*O(x^n)); polcoeff(1/(1+8*x*G^2-10*x*G^3), n)} for(n=0, 30, print1(a(n), ", ")) (PARI) {a(n)=local(G=1+x); for(i=0, n, G=1+x*G^4+x*O(x^n)); polcoeff(1/(1-2*x*G^2-10*x^2*G^6), n)} for(n=0, 30, print1(a(n), ", ")) (PARI) {a(n)=sum(k=0, n, binomial(2*n+2*k, n-k)*binomial(2*n-2*k, k))} for(n=0, 30, print1(a(n), ", ")) (PARI) {a(n)=sum(k=0, n, binomial(2*k, n-k)*binomial(4*n-2*k, k))} for(n=0, 30, print1(a(n), ", ")) (PARI) {a(n)=sum(k=0, n, binomial(4*n+2*k, n-k)*binomial(-2*k, k))} for(n=0, 30, print1(a(n), ", ")) CROSSREFS Cf. A147855, A226761, A183160, A226705, A002293. Sequence in context: A154636 A216584 A193446 * A220244 A001804 A277182 Adjacent sequences:  A226730 A226731 A226732 * A226734 A226735 A226736 KEYWORD nonn AUTHOR Paul D. Hanna, Jun 16 2013 STATUS approved

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Last modified January 18 16:27 EST 2020. Contains 331011 sequences. (Running on oeis4.)