1 + (sum of first n odd primes - n)/2.

Terms

a(0) =1a(1) =2a(2) =4a(3) =7a(4) =12a(5) =18a(6) =26a(7) =35a(8) =46a(9) =60a(10) =75a(11) =93a(12) =113a(13) =134a(14) =157a(15) =183a(16) =212a(17) =242a(18) =275a(19) =310a(20) =346a(21) =385a(22) =426a(23) =470a(24) =518a(25) =568a(26) =619a(27) =672a(28) =726a(29) =782