A117856 Number of palindromes of length n (in base 4).

3, 3, 12, 12, 48, 48, 192, 192, 768, 768, 3072, 3072, 12288, 12288, 49152, 49152, 196608, 196608, 786432, 786432, 3145728, 3145728, 12582912, 12582912, 50331648, 50331648, 201326592, 201326592, 805306368, 805306368, 3221225472, 3221225472, 12884901888

Offset: 1

Author

Martin Renner, May 02 2006

Keywords

• nonn
• base
• easy

Links

• Index entries for linear recurrences with constant coefficients, signature (0,4).

Crossrefs

Cf. A050683.

Programs

Mathematica

NestList[4#&,{3,3},20]//Flatten (* Harvey P. Dale, Dec 19 2016 *)

Formula

a(n) = 3*4^floor((n-1)/2).

From Colin Barker, Feb 15 2013: (Start)

a(n) = 4*a(n-2).

G.f.: -3*x*(x+1) / ((2*x-1)*(2*x+1)). (End)

Extensions

More terms from Colin Barker, Feb 15 2013