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 A172507 #4 Apr 28 2019 18:34:35 %S A172507 11,11,33,22,11,33,77,44,99,101,1111,303,1313,707,303,404,1717,909, %T A172507 1919,101,2121,1111,2323,606,101,1313,2727,707,2929,303 %N A172507 a(n) = numerator of fraction a/b, where gcd(a, b) = 1, whose decimal representation has the form (n).(n). %C A172507 Sequence of denominators: 10, 25, 1000, 5000, 20000, 15625, 10000000, 50000000, ... Conjecture: this sequence is not equal to the sequence A078267. %e A172507 a(6) = 33; 33/5 = 6.6. %K A172507 nonn %O A172507 1,1 %A A172507 _Jaroslav Krizek_, Feb 05 2010