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 A258493 Number of words of length 2n such that all letters of the senary 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
 132, 7007, 231868, 6191808, 146698848, 3229298919, 67773956250, 1377513928505, 27389291758920, 536341475466069, 10391807506431956, 199869644353809760, 3824918464184384952, 72954292150964887751, 1388571904028052188458, 26397789023379585277557 (list; graph; refs; listen; history; text; internal format)
 OFFSET 6,1 LINKS Alois P. Heinz, Table of n, a(n) for n = 6..750 FORMULA a(n) ~ 20^n / (384*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, 6): seq(a(n), n=6..25); CROSSREFS Column k=6 of A256117. Sequence in context: A035837 A335857 A270411 * A184893 A035818 A258394 Adjacent sequences:  A258490 A258491 A258492 * A258494 A258495 A258496 KEYWORD nonn AUTHOR Alois P. Heinz, May 31 2015 STATUS approved

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Last modified January 24 22:09 EST 2021. Contains 340414 sequences. (Running on oeis4.)