Hello SeqFans (posted Sunday, March 22nd 2020 at 23:00 Brussels time, Belgium) S = 1,2,4,80,8,81,9,10,100,90,11,12,3,31,110, 91,13,14,5,6,80,30,32,15,41,16,60,... Write under each comma the abs diff of the two digits touching the said comma. The result is a succession of digits -- S's one. (Forgive the errors that might remain in S above). Best, É.