A110400 a(1) = 1, a(2) = 21; for n>2, a(n) is the least number whose neighboring digit difference forms a(n-1) such that a(n+1) also exists.
1, 21, 132, 1031, 10032, 100031, 1000032, 10000031, 100000032, 1000000031, 10000000032, 100000000031, 1000000000032, 10000000000031, 100000000000032, 1000000000000031, 10000000000000032, 100000000000000031
Offset: 1
Examples
After 8421 two possible candidates are 91532 and 91576 but there is no number with digit difference 91576 hence the next term is 91532. 1031 is followed by 10032 because the absolute differences between the numbers 1, 0, 0, 3, 2 are 1, 0, 3, 1.
Crossrefs
Cf. A011557.
Extensions
Corrected and extended by David Wasserman, Oct 02 2005
Comments