OFFSET
0,4
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (2,1,0,-1,-4,-3,-2,-1).
FORMULA
G.f.: x^3*(1 + x) / (1 - x - x^2 - x^3 - x^4)^2.
a(n) = 2*a(n-1) + a(n-2) - a(n-4) - 4*a(n-5) - 3*a(n-6) - 2*a(n-7) - a(n-8) for n>7. - Colin Barker, Jan 18 2018
PROG
(Maxima)
a(n):=sum(sum(i*binomial(m-i, i)*binomial(m-i, n-m-i), i, 0, m), m, 0, n);
(PARI) concat(vector(2), Vec(x^2*(1 + x) / (1 - x - x^2 - x^3 - x^4)^2 + O(x^40))) \\ Colin Barker, Jan 18 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vladimir Kruchinin, Jan 17 2018
STATUS
approved