A269914 Number of ternary strings of length n with maximal run length two containing 112.

1, 5, 20, 71, 237, 761, 2377, 7278, 21945, 65375, 192861, 564387, 1640496, 4741103, 13634501, 39042437, 111379025, 316687006, 897796581, 2538530615, 7160768785, 20156241155, 56626360256, 158804376883, 444638710925, 1243115597929, 3470779612521, 9678320566654

Offset

3,2

Links

Table of n, a(n) for n=3..30.

Math StackExchange, Words built with 0,1,2

Marko Riedel, Maple code by total enumeration and by generating function.

Formula

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

Mathematica

Drop[CoefficientList[Series[x^3 (x + 1) (x^2 + x + 1)/((2 x^2 + 2 x - 1) (x^4 + 3 x^3 + 3 x^2 + x - 1)), {x, 0, 30}], x], 3] (* Michael De Vlieger, Mar 08 2016 *)

Crossrefs

Cf. A081038, A269915, A269916, A269917.

Sequence in context: A054444 A121332 A122695 * A066822 A137212 A346398

Adjacent sequences: A269911 A269912 A269913 * A269915 A269916 A269917

Keyword

nonn

Author

Marko Riedel, Mar 07 2016

Status

approved