%I #5 Aug 21 2021 15:43:01
%S 1,2,10,20,3,4,7,8,30,400,17,5,80,9,6,15,100,26,19,11,27,16,18,51,40,
%T 31,12,21,29,13,61,62,81,210,72,22,310,41,23,28,71,34,49,200,46,33,
%U 220,91,50,53,24,60,83,820,35,25,37,143,116,32,633,42,1000,194,64,45,270,218,65,305,117,352,36,14
%N There are a(n) digits between a(n) and the next copy of the string a(n) read backwards. This is the lexicographically earliest sequence of distinct positive terms with this property.
%e a(1) = 1; there is 1 digit between a(1) and the "1" of 10: this is the digit 2;
%e a(2) = 2; there are 2 digits between a(2) and the "2" of 20: they are 1 and 0;
%e a(3) = 10; there are 10 digits between a(3) and the next string "01" (formed by the terms "400, 17"): they are 2, 0, 3, 4, 7, 8, 3, 0, 4 and 0;
%e a(4) = 20; there are 20 digits between a(4) and the next string "02" (formed by the terms "100, 26"): they are 3, 4, 7, 8, 3, 0, 4, 0, 0, 1, 7, 5, 8, 0, 9, 6, 1, 5, 1 and 0;
%e a(5) = 3; there are 3 digits between a(5) and the "3" of 30: they are 4, 7 and 8;
%e a(6) = 4; there are 4 digits between a(6) and the "4" of 400: they are 7, 8, 3 and 0;
%e a(7) = 7; there are 7 digits between a(7) and the "7" of 17: they are 8, 3, 0, 4, 0, 0 and 1; etc.
%Y Cf. A346810, A303151.
%K base,nonn
%O 1,2
%A _Eric Angelini_ and _Carole Dubois_, Aug 11 2021