a(n) = prime(n+1) - (-1)^n*ceiling(n/2).

Terms

a(0) =4a(1) =4a(2) =9a(3) =9a(4) =16a(5) =14a(6) =23a(7) =19a(8) =34a(9) =26a(10) =43a(11) =35a(12) =50a(13) =40a(14) =61a(15) =51a(16) =70a(17) =58a(18) =81a(19) =63a(20) =90a(21) =72a(22) =101a(23) =85a(24) =114a(25) =90a(26) =121a(27) =95a(28) =128a(29) =112