Bernoulli number denominators, with zeros at the odd places.

Terms

a(0) =1a(1) =2a(2) =6a(3) =0a(4) =30a(5) =0a(6) =42a(7) =0a(8) =30a(9) =0a(10) =66a(11) =0a(12) =2730a(13) =0a(14) =6a(15) =0a(16) =510a(17) =0a(18) =798a(19) =0a(20) =330a(21) =0a(22) =138a(23) =0a(24) =2730a(25) =0a(26) =6a(27) =0a(28) =870a(29) =0