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%I #15 Nov 14 2020 01:50:21
%S 0,1,2,3,4,5,6,7,8,9,11,10,22,33,44,55,66,77,88,99,21,20,12,32,43,54,
%T 65,76,87,98,31,30,23,13,42,53,64,75,86,97,41,40,34,24,14,52,63,74,85,
%U 96,51,50,45,35,25,15,62,73,84,95,61,60,56,46,36,26,16,72
%N a(n) is the greatest number not yet in the sequence with the same number of digits and the same largest digit as n.
%C This sequence is a self-inverse permutation of the nonnegative integers.
%H Rémy Sigrist, <a href="/A338830/b338830.txt">Table of n, a(n) for n = 0..9999</a>
%H Rémy Sigrist, <a href="/A338830/a338830.png">Colored scatterplot of the first 10000 terms</a> (where the color is function of the largest digit of n)
%H Rémy Sigrist, <a href="/A338830/a338830.gp.txt">PARI program for A338830</a>
%H <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%F A055642(a(n)) = A055642(n).
%F A054055(a(n)) = A054055(n).
%e For n = 20:
%e - the numbers with 2 digits and largest digit 2 are: 12, 20, 21 and 22,
%e - so a(12) = 22,
%e a(20) = 21,
%e a(21) = 20,
%e a(22) = 12.
%t Block[{a = {}, f, k}, f[x_] := Max@ IntegerDigits@ x; Do[k = f[i]; AppendTo[a, SelectFirst[Range[10^# - 1, 10^(# - 1), -1] &@ Floor[1 + Log10[i]], And[f[#] == k, FreeQ[a, #]] &]], {i, 67}]; a] (* _Michael De Vlieger_, Nov 13 2020 *)
%o (PARI) See Links section.
%Y Cf. A054055, A055642, A338831.
%K nonn,base
%O 0,3
%A _Rémy Sigrist_, Nov 11 2020
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