Somos's sequence {a(4,n)} defined in comment in A018896.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =1a(8) =1a(9) =1a(10) =2a(11) =3a(12) =4a(13) =5a(14) =6a(15) =10a(16) =19a(17) =35a(18) =60a(19) =156a(20) =284a(21) =499a(22) =930a(23) =1836a(24) =7116a(25) =21586a(26) =52869a(27) =115344a(28) =356076a(29) =972840