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 A048377 #14 Jul 03 2017 01:32:25
%S A048377 0,11,222,3333,44444,555555,6666666,77777777,888888888,9999999999,110,
%T A048377 1111,11222,113333,1144444,11555555,116666666,1177777777,11888888888,
%U A048377 119999999999,2220,22211,222222,2223333,22244444,222555555,2226666666
%N A048377 Append d digits d after each digit d in decimal expansion of n.
%C A048377 a(10^n) = 11 * 10^n; A007953(a(n)) = A003132(n) + A007953(n). [_Reinhard Zumkeller_, Jul 10 2011]
%H A048377 Reinhard Zumkeller, <a href="/A048377/b048377.txt">Table of n, a(n) for n = 0..10000</a>
%e A048377 12 becomes 1 1 2 22 = 11222.
%t A048377 den[n_]:=Module[{idn=IntegerDigits[n]},FromDigits[Flatten[Table[ Table[ idn[[i]],{idn[[i]]+1}],{i,Length[idn]}]]]]; Array[den,30,0] (* _Harvey P. Dale_, Sep 04 2013 *)
%o A048377 (Haskell)
%o A048377 import Data.Char (digitToInt)
%o A048377 a048377 :: Integer -> Integer
%o A048377 a048377 n =
%o A048377 read $ concat $ zipWith replicate (map ((+ 1) . digitToInt) ns) ns
%o A048377 where ns = show n
%o A048377 -- _Reinhard Zumkeller_, Jul 10 2011
%Y A048377 Cf. A048376.
%K A048377 nonn,easy,base,nice,look
%O A048377 0,2
%A A048377 _Patrick De Geest_, Mar 15 1999