%I
%S 1,21,132,1031,10032,100031,1000032,10000031,100000032,1000000031,
%T 10000000032,100000000031,1000000000032,10000000000031,
%U 100000000000032,1000000000000031,10000000000000032,100000000000000031
%N a(1) = 1, a(2) = 21; for n>2, a(n) is the least number whose neighboring digit difference forms a(n1) such that a(n+1) also exists.
%C a(2) = 21 (chosen) and not 10 so that the sequence extends nontrivially.
%C A040115(a(n+1)) = a(n).  _David Wasserman_, Oct 02 2005
%e After 8421 two possible candidates are 91532 and 91576 but there is no number with digit difference 91576 hence the next term is 91532.
%e 1031 is followed by 10032 because the absolute differences between the numbers 1, 0, 0, 3, 2 are 1, 0, 3, 1.
%Y Cf. A011557.
%K base,easy,nonn
%O 1,2
%A _Amarnath Murthy_, Jul 29 2005
%E Corrected and extended by _David Wasserman_, Oct 02 2005
