Triangle of rencontres numbers.

Terms

a(0) =1a(1) =2a(2) =3a(3) =9a(4) =8a(5) =6a(6) =44a(7) =45a(8) =20a(9) =10a(10) =265a(11) =264a(12) =135a(13) =40a(14) =15a(15) =1854a(16) =1855a(17) =924a(18) =315a(19) =70a(20) =21a(21) =14833a(22) =14832a(23) =7420a(24) =2464a(25) =630a(26) =112a(27) =28a(28) =133496a(29) =133497