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

1,2

Comments

a(2) = 21 (chosen) and not 10 so that the sequence extends nontrivially.

A040115(a(n+1)) = a(n). - David Wasserman, Oct 02 2005

Links

Table of n, a(n) for n=1..18.

Example

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.

Sequence in context: A228283 A157624 A008384 * A308348 A089369 A328861

Adjacent sequences: A110397 A110398 A110399 * A110401 A110402 A110403

Keyword

base,easy,nonn

Author

Amarnath Murthy, Jul 29 2005

Extensions

Corrected and extended by David Wasserman, Oct 02 2005

Status

approved