A117857 Number of palindromes of length n (in base 5).

4, 4, 20, 20, 100, 100, 500, 500, 2500, 2500, 12500, 12500, 62500, 62500, 312500, 312500, 1562500, 1562500, 7812500, 7812500, 39062500, 39062500, 195312500, 195312500, 976562500, 976562500, 4882812500, 4882812500, 24414062500, 24414062500, 122070312500

Offset: 1

Author

Martin Renner, May 02 2006

Keywords

• nonn
• base
• easy

Links

• Index entries for linear recurrences with constant coefficients, signature (0,5).

Crossrefs

Cf. A050683.

Programs

Maple

A117857:=n->4*5^floor((n-1)/2): seq(A117857(n), n=1..40); # Wesley Ivan Hurt, Apr 18 2017

Mathematica

LinearRecurrence[{0,5},{4,4},40] (* or *) With[{c=NestList[ 5#&,4,20]},Riffle[ c,c]] (* Harvey P. Dale, Apr 18 2019 *)

Formula

a(n) = 4*5^floor((n-1)/2).

a(n) = 5*a(n-2). G.f.: -4*x*(x+1)/(5*x^2-1). [Colin Barker, Feb 15 2013]

Extensions

More terms from Colin Barker, Feb 15 2013