A023380 a(n+1) = a(n) converted to base 7 from base 5 (written in base 10).

5, 7, 9, 11, 15, 21, 29, 53, 101, 197, 471, 1205, 3927, 19651, 137593, 1243889, 17815781, 446377513, 21886017793, 2290044969551, 697988552388639, 733856563397342627, 3102723977467356326765, 72303720506476062470266309