OFFSET
0,2
FORMULA
From Amiram Eldar, Mar 08 2022: (Start)
Sum_{n>=1} 1/a(n) = 300 + (135*sqrt(3)/2 - 160)*Pi - 1200*log(2) + 1215*log(3)/2.
Sum_{n>=1} (-1)^(n+1)/a(n) = (60 + 160*sqrt(2) - 135*sqrt(3))*Pi + (160*sqrt(2) - 380)*log(2) - 320*sqrt(2)*log(2-sqrt(2)) - 300. (End)
EXAMPLE
a(4) = 4*5*9*13*17/30 = 1326.
MATHEMATICA
a[n_] := n*(n+1)*(2*n+1)*(3*n+1)*(4*n+1)/30; Array[a, 30, 0] (* Amiram Eldar, Mar 08 2022 *)
PROG
(PARI) a(n) = n*(n+1)*(2*n+1)*(3*n+1)*(4*n+1)/30; \\ Michel Marcus, Aug 15 2013
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Miklos Kristof, Jun 03 2004
EXTENSIONS
More terms from Michel Marcus, Aug 15 2013
STATUS
approved