%I A073013
%S A073013 1,6,37,255,1991,17598,174924,1937715,23696029,317105778,4608337064,
%T A073013 72249308222,1215116713110,21816229444012,416367513788760,
%U A073013 8415762294812355,179556294350582865,4032049130587198650
%N A073013 (1/2)*sum(k=1,n,(n+k)!/(k!)^2).
%C A073013 a(n) is odd for n = 1,3 and if n is of the form 2^m or 2^m+1 (with m>
               = 2) (i.e. a(n) is odd if n=1,3,4,5,8,9,16,17,32,33,64,65,128,129,
               256,257...)
%o A073013 (PARI) a(n)=if(n<0,0,sum(k=1,n,(n+k)!/(k!)^2)/2)
%Y A073013 Sequence in context: A154623 A005389 A080954 this_sequence A140712 A079751 
               A088312
%Y A073013 Adjacent sequences: A073010 A073011 A073012 this_sequence A073014 A073015 
               A073016
%K A073013 easy,nonn
%O A073013 1,2
%A A073013 Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 03 2002