A001446 a(n) = (4^n + 4^[ n/2 ] )/2.

10, 34, 136, 520, 2080, 8224, 32896, 131200, 524800, 2097664, 8390656, 33556480, 134225920, 536879104, 2147516416, 8589967360, 34359869440, 137439084544, 549756338176, 2199023779840, 8796095119360

Offset

2,1

Links

James Spahlinger, Table of n, a(n) for n = 2..1001

Index entries for linear recurrences with constant coefficients, signature (4,4,-16).

Formula

G.f.: x^2*(10-6x-40x^2)/((1-4x)*(1-4x^2)).

a(n) = 4*a(n-1) + 4*a(n-2) - 16*a(n-3) for n > 4. - Chai Wah Wu, Sep 10 2020

Crossrefs

Equals 2^(2[n/2]-1) * (A056450(n)+1). Cf. A001445.

Sequence in context: A232583 A068078 A067806 * A264671 A341300 A232902

Adjacent sequences: A001443 A001444 A001445 * A001447 A001448 A001449

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved