OFFSET
0,2
COMMENTS
Column k=4 of A242464.
LINKS
Fung Lam, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (1, 5, 12, 18, 22, 20, 15, 8, 3).
FORMULA
G.f.: (1 + x)*(1 + x^2)*(1 + x + x^2 )*(1 + x + x^2 + x^3 + x^4)/(1 - x - 5*x^2 - 12*x^3 - 18*x^4 - 22*x^5 - 20*x^6 - 15*x^7 - 8*x^8 - 3*x^9). (corrected by Fung Lam, May 18 2014)
EXAMPLE
a(3) = 56 because there are 64 length 3 words on {1,2,3,4} but we don't count 111, 112, 113, 114, 211, 222, 311, or 411.
MATHEMATICA
nn=23; CoefficientList[Series[1/(1-Sum[v[i]/(1+v[i])/.v[i]->(z-z^(i+1))/(1-z), {i, 1, 4}]), {z, 0, nn}], z]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Geoffrey Critzer, May 16 2014
STATUS
approved