OFFSET
0,3
COMMENTS
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Luce ETIENNE, illustration of initial terms
Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).
FORMULA
a(n) = (1/6)*Sum_{i=0..n} (i+1)*(i+2)*(2*i+3)*(n-i)^2.
G.f.: x*(1 + x)^2 / (1 - x)^7. - Colin Barker, Nov 08 2015
EXAMPLE
a(0) = 0; a(1) = 1*1; a(2) = 4*1+1*5 = 9; a(3) = 9*1+4*5+1*14 = 43.
PROG
(PARI) vector(100, n, n--; n*(n+1)*(n+2)*(n+3)*(2*n^2+6*n+7)/360) \\ Altug Alkan, Nov 08 2015
(PARI) concat(0, Vec(-x*(x+1)^2 / (x-1)^7 + O(x^100))) \\ Colin Barker, Nov 08 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Luce ETIENNE, Nov 08 2015
STATUS
approved