1,1

5-th polygonal numbers for polygons of 5^n sides divided by 5: p(5,5^x)/5, where p(n,k)=(n/2)*(n*k-k+4-2*n).

This sequence exhibits periodic digit repetition; e.g. the last digit repeats as 7, the penultimate as 4 and the antepenultimate as 2, all with a period of 1; the fourth-to-last digit repeats the sequence 1, 6 with a period of 2; the fifth-to-last repeats the sequence 3, 5, 8, 0; the sixth-to-last repeats 1, 7, 9, 5, 6, 2, 4, 0. And so on, it seems, for the other digits as the numbers grow.

Harry J. Smith, Table of n, a(n) for n=1,...,100

p := proc(n, k) (n/2)*(n*k-k+4-2*n) end: for x from 1 to 19 do p(5, 5^x)/5 od; q := proc(x) 2*5^x-3 end: for x from 1 to 19 do q(x) od;

(PARI) p(n, k) = (n/2)*(n*k-k+4-2*n) for(x=1, 19, print(p(5, 5^x)/5)) q(x) = 2*5^x-3 for(x=1, 19, print(q(x)))

(PARI) { for (n=1, 100, write("b064385.txt", n, " ", 2*5^n - 3) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Sep 13 2009]

Sequence in context: A009202 A093112 A091516 this_sequence A009260 A126635 A085352

Adjacent sequences: A064382 A064383 A064384 this_sequence A064386 A064387 A064388

nonn,easy

Daniel Dockery (drd(AT)peritus.virtualave.net), Sep 16, 2001