A037990 Numbers whose maximal base 7 run length is 3.

57, 114, 171, 228, 285, 342, 343, 399, 401, 402, 403, 404, 405, 457, 514, 571, 628, 685, 686, 743, 798, 799, 801, 802, 803, 804, 857, 914, 971, 1028, 1029, 1086, 1143, 1197, 1198, 1199, 1201, 1202, 1203, 1257, 1314, 1371, 1372