Number of set partitions of [n] that avoid 1231 and 1121.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =13a(5) =34a(6) =88a(7) =226a(8) =578a(9) =1476a(10) =3768a(11) =9620a(12) =24564a(13) =62728a(14) =160192a(15) =409096a(16) =1044744a(17) =2668048a(18) =6813600a(19) =17400400a(20) =44436688a(21) =113481248a(22) =289805440a(23) =740097568a(24) =1890041888a(25) =4826739776a(26) =12326402432