Numbers d_n used in recurrence for series-parallel numbers.

Terms

a(0) =1a(1) =2a(2) =2a(3) =6a(4) =2a(5) =18a(6) =2a(7) =46a(8) =14a(9) =126a(10) =2a(11) =454a(12) =2a(13) =1266a(14) =134a(15) =4222a(16) =2a(17) =14202a(18) =2a(19) =46406a(20) =1274a(21) =155502a(22) =2a(23) =531790a(24) =122a(25) =1792810a(26) =13802a(27) =6126334a(28) =2a(29) =21032794