%I A000989
%S A000989 0,0,1,0,0,2,1,1,2,0,0,1,0,0,3,2,2,3,1,1,2,1,1,3,2,2,3,0,0,1,0,0,2,
%T A000989 1,1,2,0,0,1,0,0,4,3,3,4,2,2,3,2,2,4,3,3,4,1,1,2,1,1,3,2,2,3,
%U A000989 1,1,2,1,1,4,3,3,4,2,2,3,2,2,4,3,3
%N A000989 3^a(n) divides C(2n,n).
%H A000989 Michael Gilleland, <a href="selfsimilar.html">Some Self-Similar Integer 
               Sequences</a>
%F A000989 a(n)=sum(k>=0, floor(2*n/3^k))-2*sum(k>=0, floor(n/3^k)) - Benoit Cloitre 
               (benoit7848c(AT)orange.fr), Aug 26 2003
%t A000989 p=3; Array[ If[ Mod[ bi=Binomial[ 2#, # ], p ]==0, Select[ FactorInteger[ 
               bi ], Function[ q, q[ [ 1 ] ]==p ], 1 ][ [ 1, 2 ] ], 0 ]&, 27*3, 
               0 ]
%o A000989 (PARI) a(n)=valuation(binomial(2*n,n),3)
%Y A000989 Sequence in context: A062979 A114781 A083890 this_sequence A132401 A104273 
               A051778
%Y A000989 Adjacent sequences: A000986 A000987 A000988 this_sequence A000990 A000991 
               A000992
%K A000989 nonn
%O A000989 0,6
%A A000989 N. J. A. Sloane (njas(AT)research.att.com), R. K. Guy (rkg(AT)cpsc.ucalgary.ca)