A339138 - OEIS

%I #10 Nov 28 2020 09:15:00

%S 0,1,10,11,21,32,20,22,31,43,30,33,41,54,40,44,51,65,50,55,61,76,60,

%T 66,71,87,70,77,81,98,80,88,91,100,99,90,110,111,101,102,42,53,52,64,

%U 62,75,72,86,82,97,92,200,112,201,103,63,74,73,85,83,96,93,300,113,301,104,95,94,84,400,114,401,105,500,115

%N Lexicographically earliest sequence of distinct nonnegative terms such that the first digit d of a(n), for n > 1, is the sum of the two closest digits of d (they are the rightmost digit of a(n-1) and the next digit on the right of d).

%C The first two digits of a(n) cannot be in ascending order.

%p a(2) = 1 and 1 is the sum of 0 + 1 (closest digits to 1);

%p a(3) = 10 and 1 is the sum of 1 + 0 (closest digits to 1);

%p a(4) = 11 and the first 1 is the sum of 0 + 1 (closest digits to 1);

%p a(5) = 21 and 2 is the sum of 1 + 1 (closest digits to 2); etc.

%Y Cf. A339139 (where the last digit is involved, instead of the first digit).

%K base,nonn

%O 1,3

%A _Eric Angelini_, Nov 25 2020