a(n) = 2*a(n-1) - 1 for n>1, a(1)=23.

Terms

a(0) =23a(1) =45a(2) =89a(3) =177a(4) =353a(5) =705a(6) =1409a(7) =2817a(8) =5633a(9) =11265a(10) =22529a(11) =45057a(12) =90113a(13) =180225a(14) =360449a(15) =720897a(16) =1441793a(17) =2883585a(18) =5767169a(19) =11534337a(20) =23068673a(21) =46137345a(22) =92274689a(23) =184549377a(24) =369098753a(25) =738197505a(26) =1476395009a(27) =2952790017