A194719 Number of n-ary words beginning with the first character of the alphabet, that can be built by inserting seven doublets into the initially empty word.

0, 1, 1716, 54573, 492724, 2467137, 8786436, 25066621, 61189668, 133071009, 264735892, 490704621, 858686676, 1432583713, 2295801444, 3554870397, 5343375556, 7826194881, 11204046708, 15718346029, 21656369652, 29356730241, 39215159236, 51690598653, 67311601764

Offset

0,3

Links

Alois P. Heinz, Table of n, a(n) for n = 0..1000

Formula

G.f.: -x*(1+1709*x+42582*x^2+146714*x^3+104077*x^4+13665*x^5+132*x^6) / (x-1)^7.

a(0) = 0, a(n) = 1+(12+(65+(208+(429+(572+429*(n-1)) * (n-1)) * (n-1)) * (n-1)) * (n-1)) * (n-1) for n>0.

Example

a(1) = 1: a^14 (with 1-ary alphabet {a}).

Maple

a:= n-> `if`(n=0, 0, (x-> 1+(12+(65+(208+(429+(572+429*x)*x)*x)
                          *x)*x)*x)(n-1)):
seq(a(n), n=0..30);

Crossrefs

Row n=7 of A183134.

Sequence in context: A260474 A222343 A318628 * A140910 A208620 A365027

Adjacent sequences: A194716 A194717 A194718 * A194720 A194721 A194722

Keyword

nonn

Author

Alois P. Heinz, Sep 02 2011

Status

approved