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

1,1

Links

Table of n, a(n) for n=1..33.

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

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)

Mathematica

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

Crossrefs

Cf. A050683.

Sequence in context: A268774 A240801 A032308 * A074850 A073055 A075780

Adjacent sequences: A117853 A117854 A117855 * A117857 A117858 A117859

Keyword

nonn,base,easy

Author

Martin Renner, May 02 2006

Extensions

More terms from Colin Barker, Feb 15 2013

Status

approved