A044539 Numbers n such that string 2,6 occurs in the base 7 representation of n but not of n+1.

20, 69, 118, 146, 167, 216, 265, 314, 363, 412, 461, 489, 510, 559, 608, 657, 706, 755, 804, 832, 853, 902, 951, 1028, 1049, 1098, 1147, 1175, 1196, 1245, 1294, 1343, 1392, 1441, 1490, 1518, 1539, 1588, 1637, 1686, 1735, 1784