A001446 - OEIS

%I #18 Feb 01 2022 23:58:35

%S 10,34,136,520,2080,8224,32896,131200,524800,2097664,8390656,33556480,

%T 134225920,536879104,2147516416,8589967360,34359869440,137439084544,

%U 549756338176,2199023779840,8796095119360

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

%H James Spahlinger, <a href="/A001446/b001446.txt">Table of n, a(n) for n = 2..1001</a>

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (4,4,-16).

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

%F a(n) = 4*a(n-1) + 4*a(n-2) - 16*a(n-3) for n > 4. - _Chai Wah Wu_, Sep 10 2020

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

%K nonn,easy

%O 2,1

%A _N. J. A. Sloane_