A288945 - OEIS

%I #13 Jul 01 2017 08:04:00

%S 1,2,11,21,22,12,13,23,24,3,25,4,31,26,5,41,27,6,51,28,7,61,29,8,71,

%T 211,212,14,32,15,42,16,52,17,62,18,72,19,81,213,214,33,215,43,216,53,

%U 217,63,218,73,219,82,111,221,222,112,113,223,224,34,35,44,36,54

%N Starting with a(1) = 1, a(n) = smallest nonnegative integer not yet in the sequence such that the first digit of a(n) is the last digit of a(n-1) plus or minus 1, with preference given to -1 when possible. The digit 0 is not allowed.

%C If a(n-1) ends in 1, a(n) must begin with 2 (i.e., a forced increase by 1).

%C There are no numbers in the sequence with first digit 9.

%e 11 is followed by 21 in the sequence since it can't be followed by a number starting with 0.

%Y Cf. A288946.

%K nonn,base

%O 1,2

%A _Enrique Navarrete_, Jun 19 2017