a(n) = Product_{k=1..floor((n-1)/2)} (1 + 4*sin(k*Pi/n)^2 + 16*sin(k*Pi/n)^4).

Terms

a(0) =1a(1) =1a(2) =1a(3) =13a(4) =7a(5) =76a(6) =39a(7) =421a(8) =217a(9) =2353a(10) =1216a(11) =13201a(12) =6825a(13) =74101a(14) =38311a(15) =415948a(16) =215047a(17) =2334781a(18) =1207089a(19) =13105441a(20) =6775552a(21) =73562593a(22) =38032081a(23) =412916701a(24) =213479175a(25) =2317756876a(26) =1198287271a(27) =13009880533a(28) =6726147337a(29) =73026206161