This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A343888 #17 May 03 2021 12:20:16
%S A343888 12,13,14,15,16,17,18,19,109,120,102,102,124,125,126,127,128,129,130,
%T A343888 130,123,103,103,135,136,137,138,139,140,140,134,124,104,104,146,147,
%U A343888 148,149,150,150,145,135,125,105,105,157,158,159,160,160,156,146,136,126,106,106,168,169,170,170
%N A343888 Smallest positive integer such that the decimal representations of a(n) and of a(n)+9n (both without leading zeros) are permutations of each other.
%C A343888 A concatenation of 10 and n provides the proof of existence and also an upper bound for a(n).
%C A343888 The bound is exact for n = 9, 90, 900, ...
%H A343888 Rémy Sigrist, <a href="/A343888/b343888.txt">Table of n, a(n) for n = 1..8999</a>
%e A343888 102 + 9*11 = 201 which is a permutation of digits of 102, and no smaller number has this feature, hence a(11)=102.
%o A343888 (PARI) a(n) = { for (v=1, oo, if (vecsort(digits(v))==vecsort(digits(v+9*n)), return (v))) } \\ _Rémy Sigrist_, May 03 2021
%Y A343888 Cf. A328447, A343852.
%K A343888 nonn,look,base
%O A343888 1,1
%A A343888 _Ivan Neretin_, May 02 2021