First occurrence of n in A220115.

Terms

a(0) =0a(1) =3a(2) =13a(3) =47a(4) =55a(5) =254a(6) =767a(7) =987a(8) =6909a(9) =16127a(10) =28657a(11) =28670a(12) =125951a(13) =196575a(14) =393213a(15) =4160255a(16) =4177911a(17) =25157623a(18) =25157631a(19) =46137325a(20) =67088375a(21) =268296191a(22) =268434303a(23) =268435455