%I A064385
%S A064385 7,47,247,1247,6247,31247,156247,781247,3906247,19531247,
%T A064385 97656247,488281247,2441406247,12207031247,61035156247,
%U A064385 305175781247,1525878906247,7629394531247,38146972656247
%N A064385 2*5^n-3.
%C A064385 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).
%C A064385 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.
%H A064385 Harry J. Smith, <a href="b064385.txt">Table of n, a(n) for n=1,...,100</
               a>
%p A064385 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;
%o A064385 (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)))
%o A064385 (PARI) { for (n=1, 100, write("b064385.txt", n, " ", 2*5^n - 3) ) } [From 
               Harry J. Smith (hjsmithh(AT)sbcglobal.net), Sep 13 2009]
%Y A064385 Sequence in context: A009202 A093112 A091516 this_sequence A009260 A126635 
               A085352
%Y A064385 Adjacent sequences: A064382 A064383 A064384 this_sequence A064386 A064387 
               A064388
%K A064385 nonn,easy
%O A064385 1,1
%A A064385 Daniel Dockery (drd(AT)peritus.virtualave.net), Sep 16, 2001