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 A120100 #11 Mar 11 2014 20:31:20
%S A120100 7,13,14,21,26,28,35,39,42,52,56,63,65,70,77,78,84,91,104,105,112,117,
%T A120100 126,130,140,143,154,156,168,175,182,189,195,208,210,224,231,234,252,
%U A120100 259,260,273,280,286,297,308,312,315,325,336,350,351,364,378,385,390
%N A120100 Integers n for which the period of the decimal expansion of 1/n is 6.
%C A120100 The initial terms in the sequence are multiples of either 7 or 13, but the sequence is not exclusively so. a(45) = 297 whose factors include neither 7 nor 13. Next is a(57) = 407 whose factors are 11 and 37.
%e A120100 a(1) = 7 because 1/7 = 0.142857142857142857+, whose repeating decimal (142857) is 6 digits long.
%e A120100 a(57) = 407 because 1/407 = 0.0024570024570024+, whose repeating decimal (002457) is 6 digits long.
%t A120100 Transpose[Select[Table[{n,Length[RealDigits[1/n][[1,-1]]]},{n,500}],#[[2]]==6&]][[1]] (* _Harvey P. Dale_, Dec 04 2010 *)
%K A120100 nonn,base
%O A120100 1,1
%A A120100 _Gil Broussard_, Aug 15 2006