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 A172671 Number of 3*n X 6 0..2 arrays with row sums 2 and column sums n. 1
 90, 202410, 747558000, 3536978063850, 19292117692187340, 115428185943399529200, 737005538936597762145600, 4937928427617947420104982250, 34335031273255183438800013252500 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Christoph Koutschan, Table of n, a(n) for n = 1..75 (first 33 terms from R. H. Hardin) Manuel Kauers and Christoph Koutschan, Some D-finite and some Possibly D-finite Sequences in the OEIS, arXiv:2303.02793 [cs.SC], 2023, pp. 19-23. FORMULA Conjectured recurrence of order 4 and degree 13: (n + 2)*(n + 3)^3*(3784*n^4 + 32164*n^3 + 100749*n^2 + 137862*n + 69678)*(n + 4)^5*a(n + 4) - (n + 2)*(n + 3)^3*(3*n + 10)*(3*n + 11)*(3799136*n^7 + 72183584*n^6 + 579689880*n^5 + 2548427912*n^4 + 6617561702*n^3 + 10141503096*n^2 + 8487349821*n + 2991586122)*a(n + 3) - 9*(n + 2)*(3*n + 7)*(3*n + 8)*(3*n + 10)*(3*n + 11)*(10844944*n^8 + 222321352*n^7 + 1973930222*n^6 + 9916013134*n^5 + 30831383530*n^4 + 60768378830*n^3 + 74160044251*n^2 + 51243135187*n + 15352797306)*a(n + 2) + 9*(3*n + 4)*(3*n + 5)*(3*n + 7)*(3*n + 8)*(3*n + 10)*(3*n + 11)*(29681696*n^7 + 504588832*n^6 + 3602458816*n^5 + 14001842392*n^4 + 32010306742*n^3 + 43078657918*n^2 + 31639900193*n + 9799573455)*a(n + 1) + 416745*(n + 1)*(3*n + 1)*(3*n + 2)*(3*n + 4)*(3*n + 5)*(3*n + 7)*(3*n + 8)*(3*n + 10)*(3*n + 11)*(3784*n^4 + 47300*n^3 + 219945*n^2 + 450988*n + 344237)*a(n) = 0. - Christoph Koutschan, Feb 26 2023 Conjecture: a(n) ~ 3^(3*n + 1/2) * 7^(3*n + 5/2) / (2^(19/2) * Pi^(5/2) * n^(5/2)), based on the recurrence by Christoph Koutschan. - Vaclav Kotesovec, Feb 27 2023 MAPLE A172671:= proc(n) local x, i, j; coeftayl(add(add(x[i]*x[j], i=1..j), j=1..6)^(3*n), [seq(x[i], i=1..6)]=[0\$6], [n\$6]) end proc: map(A172671, [\$1..10]); # Robert Israel, Jan 15 2023 MATHEMATICA Walks6D[n_Integer, steps_List] := Walks6D[n, steps] = Module[{vals = {{{{{1}}}}}, seq = {}, n0, n1}, Do[ vals = Table[ n0 = Ceiling[(nsum - n1 - n2 - n3 - n4)/2]; Join[ Table[0, {n0}], Table[Total[Function[s, pos = Reverse[Sort[{n1, n2, n3, n4, n5, nsum - n1 - n2 - n3 - n4 - n5} - s]]; If[Min[pos] < 0, 0, vals[[##]]& @@ Most[pos + 1]]] /@ steps], {n5, n0, Min[n4, nsum - n1 - n2 - n3 - n4]}] ], {n1, 0, Min[n, nsum]}, {n2, 0, Min[n1, nsum - n1]}, {n3, 0, Min[n2, nsum - n1 - n2]}, {n4, 0, Min[n3, nsum - n1 - n2 - n3]}]; If[IntegerQ[n1 = nsum/6 + 1], AppendTo[seq, vals[[n1, n1, n1, n1, n1]]]], {nsum, 2, 6 n, 2}]; Return[seq]; ]; rows = Join[Permutations[{1, 1, 0, 0, 0, 0}], Permutations[{2, 0, 0, 0, 0, 0}]]; Walks6D[20, rows] (* Christoph Koutschan, Feb 26 2023 *) CROSSREFS Sequence in context: A279442 A172572 A052277 * A066784 A135321 A135428 Adjacent sequences: A172668 A172669 A172670 * A172672 A172673 A172674 KEYWORD nonn AUTHOR R. H. Hardin, Feb 06 2010 STATUS approved

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Last modified June 5 06:51 EDT 2023. Contains 363130 sequences. (Running on oeis4.)