Number of idempotents in Identity Difference Partial Transformation semigroup.

Terms

a(0) =2a(1) =5a(2) =17a(3) =57a(4) =185a(5) =593a(6) =1901a(7) =6121a(8) =19793a(9) =64161a(10) =208085a(11) =674105a(12) =2179001a(13) =7023409a(14) =22566269a(15) =72268809a(16) =230696609a(17) =734153537a(18) =2329503653a(19) =7371475033a(20) =23267249417a(21) =73268609745a(22) =230224239437a(23) =721965697577