login
A121550
Number of ordered ways of writing n as a sum of three Fibonacci numbers (only one 1 is considered as a Fibonacci number).
13
0, 0, 1, 3, 6, 7, 9, 9, 10, 9, 12, 12, 9, 9, 10, 12, 12, 12, 12, 6, 9, 6, 12, 13, 9, 12, 12, 9, 12, 6, 12, 6, 0, 9, 6, 9, 15, 9, 13, 9, 6, 12, 9, 12, 9, 0, 12, 6, 6, 12, 0, 6, 0, 0, 9, 6, 9, 12, 9, 15, 9, 6, 13, 6, 9, 6, 0, 12, 9, 9, 12, 0, 9, 0, 0, 12, 6, 6, 6, 0, 12, 0, 0, 6, 0, 0, 0, 0, 9, 6, 9, 12
OFFSET
1,4
LINKS
FORMULA
G.f.: (Sum_{i>=2} x^Fibonacci(i))^3.
a(n) = A121548(n,3).
EXAMPLE
a(6)=7 because we have 6=1+2+3=1+3+2=2+1+3=2+3+1=3+1+2=3+2+1=2+2+2.
MAPLE
with(combinat): g:=sum(z^fibonacci(i), i=2..30)^3: gser:=series(g, z=0, 130): seq(coeff(gser, z, n), n=1..126);
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Aug 07 2006
STATUS
approved