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

2,2

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).

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)

Prog

(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

Crossrefs

Sequence in context: A151911 A037242 A158139 * A345432 A298950 A213494

Adjacent sequences: A026390 A026391 A026392 * A026394 A026395 A026396

Keyword

nonn,easy

Author

Clark Kimberling

Status

approved