Number of achiral noncrossing partitions composed of n blocks of size 4.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =5a(5) =16a(6) =31a(7) =102a(8) =213a(9) =712a(10) =1556a(11) =5255a(12) =11843a(13) =40288a(14) =92842a(15) =317548a(16) =744277a(17) =2556376a(18) =6072124a(19) =20926236a(20) =50244660a(21) =173634752a(22) =420634039a(23) =1456967358a(24) =3556069395a(25) =12341344216a(26) =30314970076a(27) =105384541314a(28) =260295610706a(29) =906188676224