%I A103972
%S A103972 1,6,12,60,264,1392,7392,41424,236640,1384512,8224896,49554816,
%T A103972 301884672,1856878080,11514915840,71915838720,451938731520,
%U A103972 2855705994240,18132621772800,115637702461440,740356410961920
%N A103972 Expansion of (1-sqrt(1-4x-20x^2))/(2x).
%C A103972 Image of c(x), the g.f. of the Catalan numbers A000108 under the mapping 
               g(x)->(1+5x)g(x(1+5x)). In general, the image of the Catalan numbers 
               under the mapping g(x)->(1+i*x)g(x(1+i*x)) is given by a(n)=sum{k=0..n, 
               i^(n-k)C(k)C(k+1,n-k)}.
%F A103972 G.f. : (1-sqrt(1-4x(1+5x))/(2x); a(n)=sum{k=0..n, 5^(n-k)C(k)C(k+1, n-k)}.
%Y A103972 Sequence in context: A117762 A104362 A123900 this_sequence A121735 A070970 
               A045780
%Y A103972 Adjacent sequences: A103969 A103970 A103971 this_sequence A103973 A103974 
               A103975
%K A103972 easy,nonn
%O A103972 0,2
%A A103972 Paul Barry (pbarry(AT)wit.ie), Feb 23 2005