Number of integers not exceeding 2^n that are impossible as sum-of-divisors of other numbers.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =15a(5) =34a(6) =75a(7) =162a(8) =337a(9) =706a(10) =1466a(11) =2995a(12) =6119a(13) =12450a(14) =25248a(15) =51158a(16) =103450a(17) =209010a(18) =421681a(19) =850322a(20) =1712673a(21) =3447970a(22) =6937759a(23) =13952296a(24) =28049834a(25) =56369395a(26) =113241087a(27) =227428919a(28) =456641954a(29) =916642515