a(n) = prime(n) - 1.

Terms

a(0) =1a(1) =2a(2) =4a(3) =6a(4) =10a(5) =12a(6) =16a(7) =18a(8) =22a(9) =28a(10) =30a(11) =36a(12) =40a(13) =42a(14) =46a(15) =52a(16) =58a(17) =60a(18) =66a(19) =70a(20) =72a(21) =78a(22) =82a(23) =88a(24) =96a(25) =100a(26) =102a(27) =106a(28) =108a(29) =112