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 A222051 Central terms in rows of triangle A220178. 2
 1, 6, 150, 4200, 131670, 4360356, 149885736, 5287716720, 190170736470, 6941694002100, 256393942704900, 9561265547652000, 359399657792284200, 13600394660797333200, 517621830467456905200, 19798076590576557847200, 760517744810283004728150, 29325625363665142395552900 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS FORMULA a(n) = (2*n+1)*binomial(2*n,n)*A222050(n), where the g.f. G(x) of A222050 satisfies: G(x) = sqrt(1 + 2*x*G(x)^4 + 3*x^2*G(x)^6). a(n) = [x^n] d^(2*n)/dx^(2*n) (1+x+x^2)^(2*n) / (2*n)!, by definition. PROG (PARI) /* As Central Terms in Rows of Triangle A220178: */ {A220178(n, k)=polcoeff(polcoeff(1/sqrt(1-2*x-3*x^2 - 4*x*y +x*O(x^n)+y*O(y^k)), n, x), k, y)} {a(n)=A220178(2*n, n)} for(n=0, 20, print1(a(n), ", ")) CROSSREFS Cf. A220178, A222050, A222052. Sequence in context: A291110 A246214 A065946 * A285747 A013296 A013301 Adjacent sequences:  A222048 A222049 A222050 * A222052 A222053 A222054 KEYWORD nonn AUTHOR Paul D. Hanna, Feb 06 2013 STATUS approved

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Last modified May 22 00:25 EDT 2019. Contains 323472 sequences. (Running on oeis4.)