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 A107286 #9 Jan 12 2019 20:45:46 %S A107286 0,1,1,1,2,1,2,1,2,3,2,1,2,1,2,3,2,1,2,1,2,3,2,1,2,5,2,3,2,1,2,1,2,3, %T A107286 2,5,2,1,2,3,2,1,2,1,2,3,2,1,2,7,2,3,2,1,2,5,2,3,2,1,2,1,2,3,2,5,2,1, %U A107286 2,3,2,1,2,1,2,3,2,7,2,1,2,3,2,1,2,5,2,3,2,1,2,7,2,3,2,5,2,1,2,3 %N A107286 a(0) = 0; for n>0, minimal prime factor of n, or 1 if n is 1 or a prime. %H A107286 Antti Karttunen, <a href="/A107286/b107286.txt">Table of n, a(n) for n = 0..20000</a> %o A107286 (PARI) a(n) = if (n==0, 0, if (n==1, 1, if (isprime(n), 1, factor(n)[1,1]))) \\ _Michel Marcus_, Jun 03 2013 %Y A107286 Cf. A020639. %K A107286 nonn,look %O A107286 0,5 %A A107286 _Giovanni Teofilatto_, May 20 2005