A026393 a(n) = T(n,n-2), where T is the array in A026386.

1, 4, 8, 17, 24, 39, 49, 70, 83, 110, 126, 159, 178, 217, 239, 284, 309, 360, 388, 445, 476, 539, 573, 642, 679, 754, 794, 875, 918, 1005, 1051, 1144, 1193, 1292, 1344, 1449, 1504, 1615, 1673, 1790, 1851, 1974, 2038, 2167, 2234, 2369, 2439, 2580, 2653, 2800

Offset: 2

Author

Clark Kimberling

Keywords

• nonn
• easy

Links

• Colin Barker, Table of n, a(n) for n = 2..1000
• Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).

Programs

PARI

Vec(x^2*(1+3*x+2*x^2+3*x^3)/((1-x)^3*(1+x)^2) + O(x^100)) \\ Colin Barker, Jan 26 2016

Formula

G.f.: x^2*(1+3*x+2*x^2+3*x^3) / ((1-x)^3*(1+x)^2). - Emeric Deutsch, Feb 18 2004

From Colin Barker, Jan 26 2016: (Start)

a(n) = (18*n^2-46*n+(-1)^n*(13-6*n)+35)/16.

a(n) = (9*n^2-26*n+24)/8 for n even.

a(n) = (9*n^2-20*n+11)/8 for n odd.

(End)