Number of idempotent n X n 0..2 matrices of rank n-1.

Terms

a(0) =1a(1) =10a(2) =51a(3) =212a(4) =805a(5) =2910a(6) =10199a(7) =34984a(8) =118089a(9) =393650a(10) =1299067a(11) =4251516a(12) =13817453a(13) =44641030a(14) =143489055a(15) =459165008a(16) =1463588497a(17) =4649045850a(18) =14721978563a(19) =46490458660a(20) =146444944821a(21) =460255540910