OFFSET
1,3
LINKS
Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-6,1).
FORMULA
a(n) = A017847(7*n-2).
a(n) = Sum_{k=0..floor(n/6)} binomial(n+k,n-2-6*k).
a(n) = 7*a(n-1) - 21*a(n-2) + 35*a(n-3) - 35*a(n-4) + 21*a(n-5) - 6*a(n-6) + a(n-7).
G.f.: x^2*(1-x)^4/((1-x)^7 - x^6).
PROG
(PARI) a(n) = sum(k=0, n\6, binomial(n+k, n-2-6*k));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Jun 23 2024
STATUS
approved