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 A258492 Number of words of length 2n such that all letters of the quinary alphabet occur at least once and are introduced in ascending order and which can be built by repeatedly inserting doublets into the initially empty word. 2
 42, 1485, 34034, 647920, 11187462, 182587701, 2880017910, 44477796451, 677940669900, 10250875770135, 154278143783022, 2316262521915440, 34742240691197182, 521131993897607925, 7822497290908844702, 117554364707534272375, 1769075045150700563052 (list; graph; refs; listen; history; text; internal format)
 OFFSET 5,1 LINKS Alois P. Heinz, Table of n, a(n) for n = 5..800 FORMULA a(n) ~ 16^n / (54*sqrt(Pi)*n^(3/2)). - Vaclav Kotesovec, Jun 01 2015 MAPLE A:= proc(n, k) option remember; `if`(n=0, 1, k/n*       add(binomial(2*n, j)*(n-j)*(k-1)^j, j=0..n-1))     end: T:= (n, k)-> add((-1)^i*A(n, k-i)/(i!*(k-i)!), i=0..k): a:= n-> T(n, 5): seq(a(n), n=5..25); MATHEMATICA A[n_, k_] := A[n, k] = If[n == 0, 1, (k/n) Sum[Binomial[2n, j] (n - j)*If[j == 0, 1, (k - 1)^j], {j, 0, n - 1}]]; T[n_, k_] := Sum[(-1)^i A[n, k - i]/(i! (k - i)!), {i, 0, k}]; a[n_] := T[n, 5]; a /@ Range[5, 25] (* Jean-François Alcover, Dec 28 2020, after Alois P. Heinz *) CROSSREFS Column k=5 of A256117. Sequence in context: A121974 A096048 A215301 * A067638 A155021 A270410 Adjacent sequences:  A258489 A258490 A258491 * A258493 A258494 A258495 KEYWORD nonn AUTHOR Alois P. Heinz, May 31 2015 STATUS approved

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Last modified January 20 04:18 EST 2021. Contains 340301 sequences. (Running on oeis4.)