a(n) = smallest prime == 1 (mod T(n)) where T(n) is the n-th triangular number (A000217).

Terms

a(0) =2a(1) =7a(2) =7a(3) =11a(4) =31a(5) =43a(6) =29a(7) =37a(8) =181a(9) =331a(10) =67a(11) =79a(12) =547a(13) =211a(14) =241a(15) =137a(16) =307a(17) =2053a(18) =191a(19) =211a(20) =463a(21) =1013a(22) =277a(23) =601a(24) =1301a(25) =3511a(26) =379a(27) =2437a(28) =1741a(29) =1861