Number of proper twice partitions of n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =6a(5) =15a(6) =45a(7) =93a(8) =223a(9) =444a(10) =944a(11) =1802a(12) =3721a(13) =6898a(14) =13530a(15) =25150a(16) =48047a(17) =87702a(18) =165173a(19) =298670a(20) =553292a(21) =995698a(22) =1815981a(23) =3242921a(24) =5872289a(25) =10406853a(26) =18630716a(27) =32879716a(28) =58391915a(29) =102371974