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A261787 a(n) is the smallest nonzero number that is not a substring of n in ternary representation.

%I A261787 #7 Feb 05 2022 16:23:32
%S A261787 1,2,1,2,2,3,1,3,1,2,2,4,2,2,3,3,3,3,1,3,1,4,3,3,1,3,1,2,2,4,2,2,4,4,
%T A261787 4,4,2,2,5,2,2,3,3,3,3,3,3,3,4,3,3,3,3,3,1,3,1,4,3,3,1,3,1,4,4,4,5,3,
%U A261787 3,3,3,3,1,3,1,4,3,3,1,3,1,2,2,4,2,2
%N A261787 a(n) is the smallest nonzero number that is not a substring of n in ternary representation.
%H A261787 Reinhard Zumkeller, <a href="/A261787/b261787.txt">Table of n, a(n) for n = 0..10000</a>
%F A261787 A261789(n) = a(A261786(n)).
%o A261787 (Haskell)
%o A261787 import Data.List (isInfixOf)
%o A261787 a261787 x = f $ tail a030341_tabf where
%o A261787    f (cs:css) = if isInfixOf cs (a030341_row x)
%o A261787                    then f css else foldr (\d v -> 3 * v + d) 0 cs
%o A261787 (PARI) ts(n) = Str(fromdigits(digits(n, 3)));
%o A261787 a(n) = my(s=ts(n), k=1); while (#strsplit(s, ts(k)) != 1, k++); k; \\ _Michel Marcus_, Feb 05 2022
%Y A261787 Cf. A007089, A030341, A261789, A261786, A261461, A261794.
%K A261787 nonn,base
%O A261787 0,2
%A A261787 _Reinhard Zumkeller_, Sep 01 2015