A024678 a(n) = positions of (p(n+1) + p(n+2))/2 in the ordered nonprimes.

2, 3, 5, 7, 9, 11, 13, 17, 20, 23, 27, 29, 31, 35, 40, 43, 46, 50, 52, 55, 59, 63, 69, 74, 76, 78, 80, 82, 90, 98, 102, 105, 110, 115, 118, 123, 127, 131, 136, 139, 144, 149, 151, 153, 159, 170, 177, 179, 181, 185, 188, 193, 200, 205, 210, 213, 216, 220, 222, 227, 238, 246, 248