A163888 a(n) = 2*a(n-2) for n > 2; a(1) = 5, a(2) = 4.

5, 4, 10, 8, 20, 16, 40, 32, 80, 64, 160, 128, 320, 256, 640, 512, 1280, 1024, 2560, 2048, 5120, 4096, 10240, 8192, 20480, 16384, 40960, 32768, 81920, 65536, 163840, 131072, 327680, 262144, 655360, 524288, 1310720, 1048576, 2621440, 2097152, 5242880

Offset: 1

Author

Klaus Brockhaus, Aug 06 2009

Keywords

• nonn

Comments

Interleaving of A020714 and A000079 without initial terms 1 and 2.

Binomial transform is A163607, second binomial transform is A163608, third binomial transform is A163609, fourth binomial transform is A163610, fifth binomial transform is A163611.

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000
• Index entries for linear recurrences with constant coefficients, signature (0, 2).

Crossrefs

Cf. A020714 (5*2^n), A000079 (powers of 2), A163607, A163608, A163609, A163610, A163611.

Programs

Magma

[ n le 2 select 6-n else 2*Self(n-2): n in [1..41] ];

Mathematica

Transpose[NestList[{Last[#],2First[#]}&,{5,4},40]] [[1]]  (* Harvey P. Dale, Mar 14 2011 *)
LinearRecurrence[{0, 2},{5, 4},41] (* Ray Chandler, Aug 14 2015 *)

PARI

x='x+O('x^50); vec(x*(5+4*x)/(1-2*x^2)) \\ G. C. Greubel, Aug 07 2017

Formula

a(n) = (7 - 3*(-1)^n)*2^((2*n-5+(-1)^n)/4).

G.f.: x*(5+4*x)/(1-2*x^2).