A025702 Index of 4^n within sequence of numbers of form 4^i*5^j.

1, 2, 4, 7, 11, 16, 22, 29, 36, 44, 53, 63, 74, 86, 99, 112, 126, 141, 157, 174, 192, 211, 230, 250, 271, 293, 316, 340, 365, 390, 416, 443, 471, 500, 530, 561, 593, 625, 658, 692, 727, 763, 800, 838, 876, 915, 955, 996, 1038, 1081, 1125, 1169, 1214, 1260, 1307, 1355