Number of partitions of [n] avoiding the pattern 12/34.

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =41a(5) =122a(6) =367a(7) =1114a(8) =3423a(9) =10670a(10) =33841a(11) =109398a(12) =361045a(13) =1217346a(14) =4195267a(15) =14775986a(16) =53172411a(17) =195396310a(18) =732806677a(19) =2802898190a(20) =10926431393a(21) =43381582538a(22) =175311002903a(23) =720640632074