Used by Polya in calculating A000598.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =1a(9) =7a(10) =37a(11) =154a(12) =558a(13) =1830a(14) =5581a(15) =16077a(16) =44251a(17) =117308a(18) =301330a(19) =753458a(20) =1840568a(21) =4405344a(22) =10355493a(23) =23953832a(24) =54614151a(25) =122903818a(26) =273320540a(27) =601273377a(28) =1309641376a(29) =2826528077