The number of order-decreasing partial isometries (of an n-chain).

Terms

a(0) =1a(1) =2a(2) =5a(3) =13a(4) =30a(5) =66a(6) =137a(7) =279a(8) =556a(9) =1104a(10) =2179a(11) =4309a(12) =8518a(13) =16886a(14) =33509a(15) =66643a(16) =132672a(17) =264492a(18) =527639a(19) =1053441a(20) =2104042a(21) =4204242a(22) =8402617a(23) =16797343a(24) =33582724a(25) =67149416a(26) =134274635a(27) =268516909a(28) =536985102a(29) =1073905134