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A207647 a(n) = Product_{k=1..n} floor((2*n+1)/k - 1).

%I A207647 #14 Jun 01 2019 15:58:10
%S A207647 1,2,4,12,48,80,360,1344,2688,8640,51840,63360,443520,1198080,2515968,
%T A207647 10886400,48384000,87736320,465315840,1134673920,3309465600,
%U A207647 11887948800,71530905600,78343372800,528817766400,1839366144000,3260694528000,15837659136000,82169502105600
%N A207647 a(n) = Product_{k=1..n} floor((2*n+1)/k - 1).
%C A207647 Forms the right border of odd-indexed rows in irregular triangle A207645.
%H A207647 Paul D. Hanna, <a href="/A207647/b207647.txt">Table of n, a(n) for n = 0..500</a>
%F A207647 a(n) = A207645(2*n+1, n).
%e A207647 Illustration of the initial terms:
%e A207647 a(1) = [3/1-1] = 2;
%e A207647 a(2) = [5/1-1]*[5/2-1] = 4;
%e A207647 a(3) = [7/1-1]*[7/2-1]*[7/3-1] = 12;
%e A207647 a(4) = [9/1-1]*[9/2-1]*[9/3-1]*[9/4-1] = 48;
%e A207647 a(5) = [11/1-1]*[11/2-1]*[11/3-1]*[11/4-1]*[11/5-1] = 80; ...
%e A207647 where [x] = floor(x).
%t A207647 Table[Product[Floor[(2n+1)/k-1],{k,n}],{n,0,30}] (* _Harvey P. Dale_, Jun 01 2019 *)
%o A207647 (PARI) {a(n)=prod(k=1,n,floor((2*n+1)/k-1))}
%o A207647 for(n=0,50,print1(a(n),", "))
%Y A207647 Cf. A207645, A207646, A207643, A207644.
%K A207647 nonn
%O A207647 0,2
%A A207647 _Paul D. Hanna_, Feb 20 2012