Write a "Look-and-Say Numbers" generator
Mathematica, 68 bytes

There's no STDIN in Mathematica, so here is a function instead

s=FromDigits/@NestList[Flatten[Reverse@@@Tally/@Split[#]]&amp;,{1},#-1]&amp;


Usage:

s[5]

&gt; {1, 11, 21, 1211, 111221}