Used by Polya in calculating A000598.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =3a(6) =8a(7) =20a(8) =46a(9) =102a(10) =220a(11) =461a(12) =948a(13) =1921a(14) =3836a(15) =7574a(16) =14810a(17) =28705a(18) =55212a(19) =105485a(20) =200300a(21) =378262a(22) =710795a(23) =1329603a(24) =2476817a(25) =4596297a(26) =8499396a(27) =15665681a(28) =28786696a(29) =52747907