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A242632
Number of n-length words w over a 9-ary alphabet {a_1,...,a_9} such that w contains never more than j consecutive letters a_j (for 1<=j<=9).
2
1, 9, 80, 711, 6318, 56143, 498896, 4433274, 39394819, 350068993, 3110771999, 27642843622, 245638961566, 2182789161071, 19396631915857, 172361736254288, 1531635402139359, 13610370004776711, 120944038906506659, 1074729088326395697, 9550223588843166996
OFFSET
0,2
LINKS
Geoffrey Critzer and Alois P. Heinz, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (7, 12, 34, 59, 109, 166, 258, 352, 483, 606, 754, 875, 1007, 1087, 1161, 1172, 1167, 1099, 1023, 895, 775, 628, 503, 371, 273, 179, 118, 66, 38, 15, 8).
FORMULA
G.f.: -(x+1) *(x^4-x^3+x^2-x+1) *(x^4+x^3+x^2+x+1) *(x^2+x+1) *(x^6+x^3+1) *(x^2+1)*(x^4+1) *(x^6+x^5+x^4+x^3+x^2+x+1) *(x^2-x+1) / (8*x^31 +15*x^30 +38*x^29 +66*x^28 +118*x^27 +179*x^26 +273*x^25 +371*x^24 +503*x^23 +628*x^22 +775*x^21 +895*x^20 +1023*x^19 +1099*x^18 +1167*x^17 +1172*x^16 +1161*x^15 +1087*x^14 +1007*x^13 +875*x^12 +754*x^11 +606*x^10 +483*x^9 +352*x^8 +258*x^7 +166*x^6 +109*x^5 +59*x^4 +34*x^3 +12*x^2 +7*x-1).
MAPLE
b:= proc(n, k, c, t) option remember;
`if`(n=0, 1, add(`if`(c=t and j=c, 0,
b(n-1, k, j, 1+`if`(j=c, t, 0))), j=1..k))
end:
a:= n-> b(n, 9, 0$2):
seq(a(n), n=0..30);
CROSSREFS
Column k=9 of A242464.
Sequence in context: A370039 A081108 A176174 * A018913 A359921 A192214
KEYWORD
nonn,easy
AUTHOR
STATUS
approved