Smallest prime divisor of 10*T(n)+1 = 5*n*(n+1)+1, where T(n) = 1 + 2 + ... + n.

Terms

a(0) =11a(1) =31a(2) =61a(3) =101a(4) =151a(5) =211a(6) =281a(7) =19a(8) =11a(9) =19a(10) =661a(11) =11a(12) =911a(13) =1051a(14) =1201a(15) =1361a(16) =1531a(17) =29a(18) =1901a(19) =11a(20) =2311a(21) =2531a(22) =11a(23) =3001a(24) =3251a(25) =3511a(26) =19a(27) =31a(28) =19a(29) =4651