Number of 312-avoiding derangements of {1,2,...,n}.

Terms

a(0) =1a(1) =0a(2) =1a(3) =1a(4) =4a(5) =10a(6) =31a(7) =94a(8) =303a(9) =986a(10) =3284a(11) =11099a(12) =38024a(13) =131694a(14) =460607a(15) =1624451a(16) =5771532a(17) =20640334a(18) =74246701a(19) =268478962a(20) =975436348a(21) =3559204700a(22) =13037907692a(23) =47931423574a(24) =176792821643a(25) =654078238224