a(n) = Sum_{k = 1..m} 2^(e_k-1) where e_k = floor(log_p_k(p_(k-1)^e_(k-1))) such that e_k > 0.

Terms

a(0) =1a(1) =3a(2) =5a(3) =11a(4) =23a(5) =39a(6) =75a(7) =151a(8) =279a(9) =559a(10) =1071a(11) =2127a(12) =4255a(13) =8351a(14) =16687a(15) =33327a(16) =66095a(17) =132191a(18) =263263a(19) =526511a(20) =1052847a(21) =2101423a(22) =4202847a(23) =8405695a(24) =16794303a(25) =33587903a(26) =67175807a(27) =134284671a(28) =268568959a(29) =537004415