

A194719


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


2



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
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OFFSET

0,3


LINKS



FORMULA

G.f.: x*(1+1709*x+42582*x^2+146714*x^3+104077*x^4+13665*x^5+132*x^6) / (x1)^7.
a(0) = 0, a(n) = 1+(12+(65+(208+(429+(572+429*(n1)) * (n1)) * (n1)) * (n1)) * (n1)) * (n1) for n>0.


EXAMPLE

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


MAPLE

a:= n> `if`(n=0, 0, (x> 1+(12+(65+(208+(429+(572+429*x)*x)*x)
*x)*x)*x)(n1)):
seq(a(n), n=0..30);


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



