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 A182396 a(n) is the least number not occurring earlier such that neighboring digits sum to 1 or 10. 1
 0, 1, 9, 10, 19, 101, 91, 910, 191, 919, 1010, 1019, 1910, 1919, 10101, 9101, 9191, 91010, 10191, 91019, 19101, 91910, 19191, 91919, 101010, 101019, 101910, 101919, 191010, 191019, 191910, 191919, 1010101, 910101, 910191, 919101, 919191 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS "Number" means "nonnegative integer", or "positive integer", starting at a(1)=1. Starting with 0 or 1, the sequence contains only the digits {0,1,9}. Starting the sequence with another digit > 1 seems to lead to a sequence alternating this initial digit and (10 minus that digit): E.g., 2,8,28,282,82,828,... or 5,55,555,5555,55555,.... Consider the function "sad" (for "sum of adjacent digits") which maps any set S and initial term x to the sequence a = sad(S,x) defined by a(0)=x, a(n+1) = the least positive integer not occurring earlier such that the sum of any two adjacent digits is in S. Then, if max(S) < 10, the sequence will be finite, ending with the first term which ends with the digit max(S) (or with x for S={}). If S={s} with 9

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Last modified May 15 13:52 EDT 2021. Contains 343920 sequences. (Running on oeis4.)