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a(n) = v(n+1)/(4*v(n)), where v = A203479.
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%I #12 Aug 29 2023 04:24:16

%S 1,20,1584,475456,541981440,2376277529600,40580860464967680,

%T 2725519037191790608384,724680197846400799531008000,

%U 766028090108619425976217272320000,3227487808644444231639810280103215104000

%N a(n) = v(n+1)/(4*v(n)), where v = A203479.

%H G. C. Greubel, <a href="/A203481/b203481.txt">Table of n, a(n) for n = 1..55</a>

%F a(n) = (1/4)*Product_{k=1..n} (2^k + 2^(n+1) - 2). - _G. C. Greubel_, Aug 28 2023

%t (* First program *)

%t f[j_]:= 2^j - 1; z = 15;

%t v[n_]:= Product[Product[f[k] + f[j], {j, k-1}], {k, 2, n}]

%t Table[v[n], {n, z}] (* A203479 *)

%t Table[v[n+1]/v[n], {n, z-1}] (* A203480 *)

%t Table[v[n+1]/(4*v[n]), {n, z-1}] (* A203481 *)

%t (* Second program *)

%t Table[Product[2^(n+1) +2^k -2, {k,n}]/4, {n,20}] (* _G. C. Greubel_, Aug 28 2023 *)

%o (Magma) [(&*[2^j + 2^(n+1) - 2: j in [1..n]])/4: n in [1..20]]; // _G. C. Greubel_, Aug 28 2023

%o (SageMath) [product(2^j+2^(n+1)-2 for j in range(1,n+1))/4 for n in range(1,21)] # _G. C. Greubel_, Aug 28 2023

%Y Cf. A203479, A203480, A093883.

%K nonn

%O 1,2

%A _Clark Kimberling_, Jan 02 2012