A085521 - OEIS

%I #29 Oct 19 2016 03:11:43

%S 1,3,27,891,114939,58963707,120816635643,989850695823099,

%T 32436417451427131131,4251538544610908358733563,

%U 2229034892015508532492061011707,4674627210894999765441323226884370171,39213619892958693087378972992951269575782139,1315790781385749638968020894900792847245520205672187

%N a(n) = Product_{k=0..n} (2^(2k+1)+1).

%C Partial products of A087289. - _Michel Marcus_, Feb 15 2014

%H Vincenzo Librandi, <a href="/A085521/b085521.txt">Table of n, a(n) for n = -1..50</a>

%H J. A. Thas, <a href="http://dx.doi.org/10.1016/S0167-5060(08)70936-1">Old and new results on spreads and ovoids of finite classical polar spaces</a>, Annals of Discrete Mathematics, Vol. 52, 1992, pp. 529-544, Combinatorics '90 — Recent Trends and Applications.

%F a(n) ~ c * 2^(n*(n+2)), where c = 2*QPochhammer(-1/2, 1/4) = 3.5167992012887276... . - _Vaclav Kotesovec_, Oct 19 2016

%t Table[Product[2^(2k+1)+1,{k,0,n}],{n,-1,15}] (* _Harvey P. Dale_, Jun 21 2011 *)

%t Table[QPochhammer[-2, 4, n + 1], {n, -1, 15}] (* _Vladimir Reshetnikov_, Oct 18 2016 *)

%o (PARI) a(n) = prod(k=0, n, 2^(2*k+1)+1); \\ _Michel Marcus_, Oct 17 2016

%K nonn

%O -1,2

%A _N. J. A. Sloane_, Jul 03 2003