[if the lines are messy, please read this message here: http://www.cetteadressecomportecinquantesignes.com/DigitEchoForbidden.htm ] Hello Math-Fun, 1) If the n-th digit of S is "d" (d chosen from 0,1,2,3,...9) then the (n+d+1)th digit of S cannot be "d" 2) Start S with a(1)=1 3) Always extend S with the smallest available integer not yet present in S and not leading to a contradiction. forbidden "d" -------> 2 forbidden "d" ---> 0 2 1 2 1 1 1 2 1 5 2 forb "d" -> 1 2 3 4 5 16 07 18 9 2 03 3 22 1 4 13 2 15 42 1 62 6 7 1 2 87 1 39 S = 1,2,3,4,5,6,7,8,9,10,20,11,22,13,30,12,21,14,23,15,24,16,26,17,25,18,27,19,28,29,31,32,40,... S is obviously finite (the term 9876543210 blocks any extension, for example); what is the last term of S? Best, É.