Number of set partitions of [n] with symmetric block size list.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =7a(5) =9a(6) =47a(7) =80a(8) =492a(9) =985a(10) =7197a(11) =16430a(12) =139316a(13) =361737a(14) =3425683a(15) =9939134a(16) =103484333a(17) =329541459a(18) =3747921857a(19) =12980700318a(20) =159811532315a(21) =598410986533