Number of partitions of an n-element set avoiding the pattern 12|3.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =19a(6) =53a(7) =160a(8) =512a(9) =1753a(10) =6431a(11) =25072a(12) =103022a(13) =444145a(14) =2004281a(15) =9447784a(16) =46407476a(17) =236950873a(18) =1254862955a(19) =6880495528a(20) =38999582018a(21) =228195894313