A188580 Number of words of length n over an alphabet of size 5 which do not contain a run of 5 identical letters.

1, 5, 25, 125, 625, 3120, 15580, 77800, 388500, 1940000, 9687520, 48375280, 241565200, 1206272000, 6023600000, 30079249920, 150202748480, 750047481600, 3745412320000, 18702967200000, 93394519000320, 466371784007680, 2328858730112000, 11629312001280000, 58071748137600000, 289985162611998720, 1448060325923962880, 7230986194699366400

Offset: 0

Author

N. J. A. Sloane, Apr 09 2011

Keywords

• nonn
• easy

Comments

This is the case M=5 of the general problem mentioned in A188714.

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A040000, A121907, A188714.

Programs

Maple

See A188714.

Mathematica

CoefficientList[Series[(1 + x + x^2 + x^3 + x^4)/(1 - 4*x - 4*x^2 - 4*x^3 - 4*x^4), {x, 0, 40}], x] (* Vincenzo Librandi, Dec 09 2012 *)

Formula

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