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A194716 Number of n-ary words beginning with the first character of the alphabet, that can be built by inserting four doublets into the initially empty word. 2
0, 1, 35, 181, 523, 1145, 2131, 3565, 5531, 8113, 11395, 15461, 20395, 26281, 33203, 41245, 50491, 61025, 72931, 86293, 101195, 117721, 135955, 155981, 177883, 201745, 227651, 255685, 285931, 318473, 353395, 390781, 430715, 473281, 518563, 566645, 617611 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

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

FORMULA

G.f.: x*(1+31*x+47*x^2+5*x^3) / (x-1)^4.

a(0) = 0, a(n) = 1+(6+(14+14*(n-1))*(n-1))*(n-1) for n>0.

EXAMPLE

a(2) = 35: aaaaaaaa, aaaaaabb, aaaaabba, aaaabaab, aaaabbaa, aaaabbbb, aaabaaba, aaabbaaa, aaabbabb, aaabbbba, aabaaaab, aabaabaa, aabaabbb, aababbab, aabbaaaa, aabbaabb, aabbabba, aabbbaab, aabbbbaa, aabbbbbb, abaaaaba, abaabaaa, abaababb, abaabbba, ababbaba, abbaaaaa, abbaaabb, abbaabba, abbabaab, abbabbaa, abbabbbb, abbbaaba, abbbbaaa, abbbbabb, abbbbbba (with 2-ary alphabet {a,b}).

MAPLE

a:= n-> `if`(n=0, 0, (x-> 1+(6+(14+14*x)*x)*x)(n-1)):

seq(a(n), n=0..40);

CROSSREFS

Row n=4 of A183134.

Sequence in context: A319042 A033851 A219825 * A220047 A101954 A220201

Adjacent sequences:  A194713 A194714 A194715 * A194717 A194718 A194719

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Sep 02 2011

STATUS

approved

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Last modified February 23 08:00 EST 2019. Contains 320420 sequences. (Running on oeis4.)