Used by Polya in calculating A000598.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =1a(7) =5a(8) =19a(9) =63a(10) =184a(11) =503a(12) =1300a(13) =3229a(14) =7748a(15) =18106a(16) =41327a(17) =92521a(18) =203601a(19) =441466a(20) =944618a(21) =1997726a(22) =4180405a(23) =8665024a(24) =17805427a(25) =36299704a(26) =73468100a(27) =147704332a(28) =295122569a(29) =586304222