a(1)=1, a(n)=a(n-1) plus the second prime greater than a(n-1).

Terms

a(0) =1a(1) =4a(2) =11a(3) =28a(4) =59a(5) =126a(6) =257a(7) =526a(8) =1073a(9) =2164a(10) =4367a(11) =8758a(12) =17537a(13) =35088a(14) =70187a(15) =140388a(16) =280795a(17) =561612a(18) =1123315a(19) =2246642a(20) =4493329a(21) =8986712a(22) =17973451a(23) =35946942a(24) =71893933a(25) =143787890a(26) =287575797a(27) =575151614a(28) =1150303251a(29) =2300606554