%I A023000
%S A023000 0,1,8,57,400,2801,19608,137257,960800,6725601,47079208,329554457,
%T A023000 2306881200,16148168401,113037178808,791260251657,5538821761600,
%U A023000 38771752331201,271402266318408,1899815864228857,13298711049602000
%N A023000 (7^n - 1)/6.
%C A023000 7^(floor(7^n/6)) is the highest power of 7 dividing (7^n)! - Benoit Cloitre 
               (benoit7848c(AT)orange.fr), Feb 04 2002
%C A023000 Except for the first term, a(n)=7*a(n-1)+1 (with a(1)=1) [From Vincenzo 
               Librandi (vincenzo.librandi(AT)tin.it), Oct 29 2009]
%H A023000 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               Repunit.html">Link to a section of The World of Mathematics.</a>
%F A023000 ((4+sqrt9)^n-(4-sqrt9)^n/6. Offset 1. a(3)=57 [From Al Hakanson (hawkuu(AT)gmail.com), 
               Jan 07 2009]
%F A023000 a(n)=8*a(n-1)-7*a(n-2). G.f.: x/((1-x)(1-7x)). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), 
               Jun 21 2009]
%p A023000 a:=n->sum(7^(n-j),j=1..n): seq(a(n), n=0..20); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), 
               Jan 04 2007
%t A023000 lst={};Do[p=(7^n-1)/6;AppendTo[lst, p], {n, 0, 5!}];lst [From Vladimir 
               Orlovsky (4vladimir(AT)gmail.com), Sep 29 2008]
%o A023000 (Other) sage: [lucas_number1(n,8,7) for n in xrange(0, 21)]# [From Zerinvary 
               Lajos (zerinvarylajos(AT)yahoo.com), Apr 23 2009]
%o A023000 (Other) sage: [gaussian_binomial(n,1,7) for n in xrange(0,21)] # [From 
               Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), May 28 2009]
%Y A023000 Sequence in context: A079926 A108666 A164031 this_sequence A097114 A022038 
               A015453
%Y A023000 Adjacent sequences: A022997 A022998 A022999 this_sequence A023001 A023002 
               A023003
%K A023000 easy,nonn
%O A023000 0,3
%A A023000 David W. Wilson (davidwwilson(AT)comcast.net)