Number of permutations of [n] with 3 sequences.

Terms

a(0) =0a(1) =10a(2) =58a(3) =236a(4) =836a(5) =2766a(6) =8814a(7) =27472a(8) =84472a(9) =257522a(10) =780770a(11) =2358708a(12) =7108908a(13) =21392278a(14) =64307926a(15) =193185944a(16) =580082144a(17) =1741295034a(18) =5225982282a(19) =15682141180a(20) =47054812180a(21) =141181213790a(22) =423577195838