A018860 4^a(n) is smallest power of 4 beginning with n.

0, 4, 39, 1, 51, 3, 23, 53, 78, 5, 25, 40, 60, 75, 90, 2, 17, 27, 42, 52, 62, 72, 82, 92, 4, 9, 19, 24, 34, 39, 49, 54, 59, 64, 74, 79, 84, 89, 94, 6, 11, 16, 21, 119, 26, 31, 36, 41, 46, 51, 56, 154, 61, 66, 71, 267, 76, 81, 86, 184, 91, 96, 194, 3, 8, 204, 13, 18, 116, 23, 317, 28