A025731 Index of 8^n within sequence of numbers of form 7^i*8^j.

1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 137, 155, 174, 194, 215, 237, 260, 284, 309, 335, 362, 390, 419, 449, 480, 513, 547, 582, 618, 655, 693, 732, 772, 813, 855, 898, 942, 987, 1033, 1081, 1130, 1180, 1231, 1283, 1336, 1390, 1445, 1501, 1558, 1616