A026381 T(n,n-2), where T is the array in A026374.

1, 4, 11, 17, 30, 39, 58, 70, 95, 110, 141, 159, 196, 217, 260, 284, 333, 360, 415, 445, 506, 539, 606, 642, 715, 754, 833, 875, 960, 1005, 1096, 1144, 1241, 1292, 1395, 1449, 1558, 1615, 1730, 1790, 1911, 1974, 2101, 2167, 2300

Offset

2,2

Links

Reinhard Zumkeller, 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.: z^2*(1+3z+5z^2)/[(1-z)^3*(1+z)^2]. - Emeric Deutsch, Jan 25 2004

a(n) ~ 9*n^2/8. - Charles R Greathouse IV, May 29 2026

Mathematica

Drop[CoefficientList[Series[z^2(1+3z+5z^2)/((1-z)^3(1+z)^2), {z, 0, 50}], z], 2] (* Harvey P. Dale, Dec 31 2021 *)
(* Alternative: *)
LinearRecurrence[{1, 2, -2, -1, 1}, {1, 4, 11, 17, 30}, 50] (* Harvey P. Dale, Dec 31 2021 *)

Prog

(Haskell)
a026381 = flip a026374 2  -- Reinhard Zumkeller, Feb 22 2014
(PARI) a(n)=(9*n^2+(-14-n%2*6)*n+[0, 11][n%2+1])/8 \\ Charles R Greathouse IV, May 29 2026

Crossrefs

Cf. A026374.

Sequence in context: A160907 A003146 A063237 * A063556 A133725 A050395

Adjacent sequences: A026378 A026379 A026380 * A026382 A026383 A026384

Keyword

nonn,easy,changed

Author

Clark Kimberling

Status

approved