A027138 a(n) = Sum_{k=0..2n} (k+1) * A027113(n, 2n-k).

1, 7, 26, 85, 264, 803, 2422, 7281, 21860, 65599, 196818, 590477, 1771456, 5314395, 15943214, 47829673, 143489052, 430467191, 1291401610, 3874204869, 11622614648, 34867843987, 104603532006, 313810596065, 941431788244, 2824295364783, 8472886094402

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• easy

Links

• Colin Barker, Table of n, a(n) for n = 1..1000
• Index entries for linear recurrences with constant coefficients, signature (5,-7,3).

Programs

PARI

Vec(-x*(x^3-2*x^2+2*x+1)/((x-1)^2*(3*x-1)) + O(x^50)) \\ Colin Barker, Jul 11 2015

Formula

For n>1, a(n) = 10*3^(n-2) - n - 1.

For n>4, a(n) = 5*a(n-1) - 7*a(n-2) + 3*a(n-3). - Colin Barker, Jul 11 2015

G.f.: -x*(x^3-2*x^2+2*x+1) / ((x-1)^2*(3*x-1)). - Colin Barker, Jul 11 2015