Number of set partitions of [n] into two blocks with distinct sizes.

Terms

a(0) =3a(1) =4a(2) =15a(3) =21a(4) =63a(5) =92a(6) =255a(7) =385a(8) =1023a(9) =1585a(10) =4095a(11) =6475a(12) =16383a(13) =26332a(14) =65535a(15) =106761a(16) =262143a(17) =431909a(18) =1048575a(19) =1744435a(20) =4194303a(21) =7036529a(22) =16777215a(23) =28354131a(24) =67108863a(25) =114159427a(26) =268435455a(27) =459312151a(28) =1073741823a(29) =1846943452