a(n) = denominator(B°(2*n))/4 where the B°(n) are Zagier's modified Bernoulli numbers.

Terms

a(0) =6a(1) =20a(2) =315a(3) =280a(4) =66a(5) =3003a(6) =78a(7) =9520a(8) =305235a(9) =20900a(10) =138a(11) =19734a(12) =6a(13) =7540a(14) =15575175a(15) =590240a(16) =6a(17) =107666559a(18) =222a(19) =11996600a(20) =50536395a(21) =19780a(22) =282a(23) =31534932a(24) =66a(25) =1060a(26) =48532365a(27) =738920a(28) =354a(29) =83912718435