A025722 Index of 7^n within sequence of numbers of form 4^i*7^j.

1, 3, 6, 11, 17, 25, 34, 44, 56, 69, 84, 100, 117, 136, 156, 178, 201, 225, 251, 278, 307, 337, 368, 401, 435, 471, 508, 546, 586, 627, 670, 714, 759, 806, 854, 904, 955, 1007, 1061, 1116, 1173, 1231, 1290, 1351, 1413, 1477, 1542, 1608, 1676, 1745, 1816, 1888