OFFSET
0,10
COMMENTS
Number of compositions of n into parts 2 and 7.
LINKS
Index entries for linear recurrences with constant coefficients, signature (0,1,0,0,0,0,1).
FORMULA
a(n) = a(n-2) + a(n-7).
a(n) = A007380(n-7) for n >= 8.
PROG
(PARI) my(N=70, x='x+O('x^N)); Vec(1/(1-x^2-x^7))
(PARI) a(n) = sum(k=0, n\7, ((n-5*k)%2==0)*binomial((n-5*k)/2, k));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Feb 02 2024
STATUS
approved