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 A257829 #15 Mar 18 2018 14:30:56
%S A257829 1,2,3,4,5,6,7,8,9,45,566,1500,2250,3750,18000,383333,4428571,
%T A257829 11250000,788888888,1000000000,2000000000,3000000000,4000000000,
%U A257829 5000000000,6000000000,7000000000,8000000000,9000000000,44545454545,358333333333,4461538461538
%N A257829 The decimal representation of the average of the digits of n starts with the digits of n.
%C A257829 The sequence is infinite since it contains all the numbers m*10^(10^k-1), for 1 <= m <= 9 and k >= 0.
%H A257829 Giovanni Resta, <a href="/A257829/b257829.txt">Table of n, a(n) for n = 1..876</a> (terms < 10^1000)
%e A257829 566 is a term since the mean of its digits is (5+6+6)/3 = 17/3 and the first 3 digits of 17/3 = 5.6666... are 566. - corrected by _Joseph L. Wetherell_, Mar 17 2018
%t A257829 (* outputs terms with at most 100 digits *) sol[nd_] := Block[{z = Range[9 nd]/nd, x}, x = FromDigits /@ First /@ RealDigits[z, 10, nd]; x[[Select[Range@ Length@x, z[[#]] == Mean@ IntegerDigits@x[[#]] &]]]]; Union@ Flatten@Array[sol, 100]
%Y A257829 Cf. A257830.
%K A257829 base,nonn
%O A257829 1,2
%A A257829 _Eric Angelini_ and _Giovanni Resta_, May 10 2015