This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

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