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 A275049 Diagonal of the rational function 1/(1-(wxz + xyz + wy + xy + z)) [even-indexed terms only]. 1
 1, 30, 3870, 698880, 146881350, 33664290660, 8161119046080, 2057838873742080, 534207274296708870, 141819633092233024500, 38325111684989079770820, 10507683011039968126464000, 2915637485437466384104036800, 817228372649330361131497411200 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Odd-order terms are zero since R(x,y,z,w) = R(-x,-y,z,-w), where R(x,y,z,w) = 1/(1-(w*x*z + x*y*z + w*y + x*y + z)). LINKS Gheorghe Coserea and Alois P. Heinz, Table of n, a(n) for n = 0..402 (first 34 terms from Gheorghe Coserea) A. Bostan, S. Boukraa, J.-M. Maillard, J.-A. Weil, Diagonals of rational functions and selected differential Galois groups, arXiv preprint arXiv:1507.03227 [math-ph], 2015. S. Eger, On the Number of Many-to-Many Alignments of N Sequences, arXiv:1511.00622 [math.CO], 2015. FORMULA a(n) = [(xyzw)^(2n)] 1/(1-(w*x*z + x*y*z + w*y + x*y + z)). 0 = (10624*x^3-3427384*x^5+24111324*x^7-10234350*x^9-1476225*x^11)*y'''' + (42496*x^2-30355056*x^4+182389536*x^6-140729400*x^8-14762250*x^10)*y''' + (10624*x-62747592*x^3+309393468*x^5-459003510*x^7-36577575*x^9)*y'' + (-10624-25151544*x^2+117851940*x^4-351676890*x^6-21159225*x^8)*y'  + (11243520*x^3-29496960*x^5-1166400*x^7)*y, where y(x) = A(x^2). From Vaclav Kotesovec, Aug 03 2016: (Start) Recurrence: 4*(n-1)*n^3*(238*n^2 - 663*n + 457)*a(n) = 2*(n-1)*(150416*n^5 - 644640*n^4 + 1020351*n^3 - 734334*n^2 + 237007*n - 26880)*a(n-1) - 9*(3*n - 5)^2*(3*n - 4)^2*(238*n^2 - 187*n + 32)*a(n-2). a(n) ~ sqrt(1 + 11/(4*sqrt(7))) * (158 + 119*sqrt(7)/2)^n / (2*Pi^(3/2)*n^(3/2)). (End) a(n) = Sum_{k = 0..n} C(3*n+k,k)*C(n,k)*(3*n)!/n!^3 (apply Eger, Theorem 3 to the set of column vectors S = {[0,0,1,0], [1,1,0,0], [0,1,0,1], [1,1,1,0], [1,0,1,1]}). - Peter Bala, Jan 27 2018 EXAMPLE 1 + 30*x^2 + 3870*x^4 + 698880*x^6 + ... MAPLE with(combinat): seq(add(binomial(3n+k, k)*binomial(n, k)*(3n)!/n!^3, k = 0..n), n = 0..20); # Peter Bala, Jan 27 2018 MATHEMATICA a[n_] := (3n)! Hypergeometric2F1[-n, 3n + 1, 1, -1]/n!^3; a /@ Range[0, 20] (* Jean-François Alcover, Feb 29 2020, after Peter Bala *) PROG (PARI) my(x='x, y='y, z='z, w='w); R = 1/(1-(w*x*z+x*y*z+w*y+x*y+z)); diag(n, expr, var) = {   my(a = vector(n));   for (i = 1, #var, expr = taylor(expr, var[#var - i + 1], n));   for (k = 1, n, a[k] = expr;        for (i = 1, #var, a[k] = polcoeff(a[k], k-1)));   return(a); }; diag(23, R, [x, y, z, w]) CROSSREFS Cf. A268545-A268555. Sequence in context: A159993 A153470 A289247 * A127849 A166845 A166834 Adjacent sequences:  A275046 A275047 A275048 * A275050 A275051 A275052 KEYWORD nonn,easy AUTHOR Gheorghe Coserea, Jul 19 2016 STATUS approved

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Last modified July 31 22:27 EDT 2021. Contains 346377 sequences. (Running on oeis4.)