A277670 Number of n-length words over a 7-ary alphabet {a_1,a_2,...,a_7} avoiding consecutive letters a_i, a_{i+1}.

1, 7, 43, 264, 1621, 9953, 61112, 375231, 2303939, 14146313, 86859145, 533319959, 3274614074, 20106311704, 123453866991, 758013577995, 4654245334143, 28577324020619, 175466351588409, 1077373112945523, 6615130559166437, 40617267861064920, 249392273325801363

Offset: 0

Author

Alois P. Heinz, Oct 26 2016

Keywords

• nonn
• easy

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (7,-6,5,-4,3,-2,1)

Crossrefs

Column k=7 of A277666.

Programs

Maple

a:= proc(n) option remember; `if`(n<0, 0, `if`(n=0, 1,
      -add((-1)^j*(8-j)*a(n-j), j=1..7)))
    end:
seq(a(n), n=0..25);

Formula

G.f.: 1/(1 + Sum_{j=1..7} (8-j)*(-x)^j).