A075339 - OEIS

A075339

a(1) = 1, a(2n) = smallest composite number obtained by adding a prime to a(2n-1). a(2n+1) = the smallest prime obtained by adding a composite number to a(2n).

1, 4, 13, 15, 19, 21, 29, 32, 41, 44, 53, 55, 59, 62, 71, 74, 83, 85, 89, 91, 97, 99, 103, 105, 109, 111, 127, 129, 137, 140, 149, 152, 167, 169, 173, 175, 179, 182, 191, 194, 227, 230, 239, 242, 251, 253, 257, 259, 263, 265, 269, 272, 281, 284, 293, 295, 307