%I A129890
%S A129890 1,5,33,279,2895,35685,509985,8294895,151335135,3061162125,68000295825,
%T A129890 1645756410375,43105900812975,1214871076343925,36659590336994625,
%U A129890 1179297174137457375,40288002704636061375,1456700757237661060125
%N A129890 Difference between the double factorial of the n-th nonnegative even 
               number and the double factorial of the n-th nonnegative odd number.
%F A129890 a(n)=(2*n)!!-(2*n-1)!!, with n>=1.
%e A129890 2!!-1!!=2-1=1
%e A129890 4!!-3!!=8-3=5
%e A129890 6!!-5!!=48-15=33
%p A129890 P:=proc(n) local a,i,j,k,w; for i from 1 by 1 to n do k:=product(2*j, 
               j=1..i); w:=product(2*j-1,j=1..i); a:=k-w; print(a) od; end: P(20);
%Y A129890 Cf. A122649.
%Y A129890 Sequence in context: A087633 A135075 A049377 this_sequence A120733 A144792 
               A001828
%Y A129890 Adjacent sequences: A129887 A129888 A129889 this_sequence A129891 A129892 
               A129893
%K A129890 easy,nonn
%O A129890 0,2
%A A129890 Paolo P. Lava & Giorgio Balzarotti (ppl(AT)spl.at), Jun 04 2007