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A117857 Number of palindromes of length n (in base 5). 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..31.

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

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]

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 *)

CROSSREFS

Cf. A050683.

Sequence in context: A035413 A261568 A087213 * A165559 A180967 A231884

Adjacent sequences:  A117854 A117855 A117856 * A117858 A117859 A117860

KEYWORD

nonn,base,easy

AUTHOR

Martin Renner, May 02 2006

EXTENSIONS

More terms from Colin Barker, Feb 15 2013

STATUS

approved

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Last modified December 15 04:23 EST 2019. Contains 329991 sequences. (Running on oeis4.)