OFFSET
1,1
COMMENTS
This sequence gives the minimum value such that the concatenation of the absolute value of the differences between its adjacent digits give n. Some values of n have no ancestor, see A271639. These are given the value -1 in this sequence.
EXAMPLE
a(1) = 10 as |1 - 0| = 1, and 10 is the smallest such number.
a(9) = 90 as |9 - 0| = 9, and 90 is the smallest such number
a(10) = 100 as |1 - 0| = 1, and |0 - 0| = 0, giving a concatenation of 10. 100 is the smallest such number.
a(48) = 408 as |4 - 0| = 4 and |0 - 8| = 8, giving a concatenation of 48. 408 is the smallest such number.
MATHEMATICA
max = 60; seq = Table[-1, {max}]; count = 0; n = 1; While[count < max && n <= 10^(1 + Ceiling[Log10[max]]), index = FromDigits @ Abs @ Differences @ IntegerDigits[n]; If[index <= max && seq[[index]] < 0, count++; seq[[index]] = n]; n++]; seq (* Amiram Eldar, Nov 29 2019 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Scott R. Shannon, Nov 29 2019
STATUS
approved