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A242630
Number of n-length words w over a 7-ary alphabet {a_1,...,a_7} such that w contains never more than j consecutive letters a_j (for 1<=j<=7).
2
1, 7, 48, 329, 2254, 15443, 105804, 724892, 4966431, 34026362, 233123809, 1597194268, 10942809918, 74972150416, 513654479985, 3519185768909, 24110893526041, 165190252745398, 1131763100053353, 7754015102916294, 53124854674462893, 363972747889200054
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 (4, 13, 33, 61, 106, 157, 220, 277, 331, 364, 382, 369, 340, 289, 233, 170, 117, 70, 39, 17, 6).
FORMULA
G.f.: -(x+1) *(x^2+1) *(x^4+1) *(x^6+x^5+x^4+x^3+x^2+x+1) *(x^2+x+1) *(x^2-x+1) *(x^4+x^3+x^2+x+1) / (6*x^21 +17*x^20 +39*x^19 +70*x^18 +117*x^17 +170*x^16 +233*x^15 +289*x^14 +340*x^13 +369*x^12 +382*x^11 +364*x^10 +331*x^9 +277*x^8 +220*x^7 +157*x^6 +106*x^5 +61*x^4 +33*x^3 +13*x^2 +4*x-1).
CROSSREFS
Column k=7 of A242464.
Sequence in context: A289785 A036829 A164591 * A004187 A180167 A341425
KEYWORD
nonn,easy
AUTHOR
STATUS
approved