A043251 Numbers n such that 5 and 6 occur juxtaposed in the base 10 representation of n but not of n-1.

56, 65, 156, 165, 256, 265, 356, 365, 456, 465, 556, 560, 650, 665, 756, 765, 856, 865, 956, 965, 1056, 1065, 1156, 1165, 1256, 1265, 1356, 1365, 1456, 1465, 1556, 1560, 1650, 1665, 1756, 1765, 1856, 1865, 1956, 1965, 2056