OFFSET
0,2
COMMENTS
Also the number of compositions of n where each part i is marked with a word of length i over a denary alphabet whose letters appear in alphabetical order.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..850
Index entries for linear recurrences with constant coefficients, signature (20, -90, 240, -420, 504, -420, 240, -90, 20, -2).
FORMULA
G.f.: (1-x)^10/(2*(1-x)^10-1).
a(n) = A261780(n,10).
a(n) = Sum_{k>=0} (1/2)^(k+1) * binomial(n-1+10*k,n). - Seiichi Manyama, Aug 06 2024
MAPLE
a:= proc(n) option remember; `if`(n=0, 1,
add(a(n-j)*binomial(j+9, 9), j=1..n))
end:
seq(a(n), n=0..20);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Alois P. Heinz, Sep 01 2015
STATUS
approved