(n-th 6k+1 prime plus n-th 6k+5 prime)/6.

Terms

a(0) =2a(1) =4a(2) =6a(3) =9a(4) =11a(5) =14a(6) =18a(7) =20a(8) =22a(9) =25a(10) =30a(11) =32a(12) =35a(13) =39a(14) =42a(15) =47a(16) =49a(17) =52a(18) =58a(19) =61a(20) =63a(21) =67a(22) =70a(23) =76a(24) =79a(25) =85a(26) =88a(27) =90a(28) =95a(29) =97