a(n) = digsum(2^a(n-1)) with a(0) = 0.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =7a(5) =11a(6) =14a(7) =22a(8) =25a(9) =29a(10) =41a(11) =50a(12) =76a(13) =106a(14) =142a(15) =214a(16) =313a(17) =380a(18) =508a(19) =691a(20) =875a(21) =1184a(22) =1687a(23) =2243a(24) =3164a(25) =4126a(26) =5578a(27) =7855a(28) =10676a(29) =13981