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A207646 Product_{k=1..n} floor(2*n/k - 1).

%I A207646 #22 Aug 27 2017 13:16:19
%S A207646 1,1,3,10,21,72,330,468,2520,8160,20520,60480,318780,504000,2426112,
%T A207646 10523520,21092400,53222400,452390400,506373120,3226728960,
%U A207646 11604902400,21299241600,76640256000,431500608000,844958822400,3197988864000,10492449177600,38109367296000
%N A207646 Product_{k=1..n} floor(2*n/k - 1).
%C A207646 Forms the right border of even-indexed rows in irregular triangle A207645.
%H A207646 Paul D. Hanna, <a href="/A207646/b207646.txt">Table of n, a(n) for n = 0..500</a>
%F A207646 a(n) = A207645(2*n, n).
%e A207646 Illustration of the initial terms:
%e A207646 a(1) = [2/1-1] = 1;
%e A207646 a(2) = [4/1-1]*[4/2-1] = 3;
%e A207646 a(3) = [6/1-1]*[6/2-1]*[6/3-1] = 10;
%e A207646 a(4) = [8/1-1]*[8/2-1]*[8/3-1]*[8/4-1] = 21;
%e A207646 a(5) = [10/1-1]*[10/2-1]*[10/3-1]*[10/4-1]*[10/5-1] = 72; ...
%e A207646 where [x] = floor(x).
%t A207646 Table[Product[Floor[(2n)/k-1],{k,n}],{n,0,30}] (* _Harvey P. Dale_, Aug 27 2017 *)
%o A207646 (PARI) {a(n)=prod(k=1,n,floor(2*n/k-1))}
%o A207646 for(n=0,50,print1(a(n),", "))
%o A207646 (PARI) a(n)=n*=2;prod(k=1,n/3,n\k-1) \\ _Charles R Greathouse IV_, Feb 20 2012
%Y A207646 Cf. A207645, A207647, A207643, A207644.
%K A207646 nonn
%O A207646 0,3
%A A207646 _Paul D. Hanna_, Feb 20 2012