A061767 a(1) = 4; a(n) = smallest composite number of the form k*n + 1.

4, 9, 4, 9, 6, 25, 8, 9, 10, 21, 12, 25, 14, 15, 16, 33, 18, 55, 20, 21, 22, 45, 24, 25, 26, 27, 28, 57, 30, 91, 32, 33, 34, 35, 36, 145, 38, 39, 40, 81, 42, 85, 44, 45, 46, 93, 48, 49, 50, 51, 52, 105, 54, 55, 56, 57, 58, 117, 60, 121, 62, 63, 64, 65, 66, 133, 68, 69, 70