Squares of Bernoulli number denominators A027642.

Terms

a(0) =1a(1) =4a(2) =36a(3) =1a(4) =900a(5) =1a(6) =1764a(7) =1a(8) =900a(9) =1a(10) =4356a(11) =1a(12) =7452900a(13) =1a(14) =36a(15) =1a(16) =260100a(17) =1a(18) =636804a(19) =1a(20) =108900a(21) =1a(22) =19044a(23) =1a(24) =7452900a(25) =1a(26) =36a(27) =1a(28) =756900a(29) =1