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 A119909 #8 Feb 06 2015 11:46:29 %S A119909 1,2,4,5,7,22,43,131,394 %N A119909 Numbers n such that n and n^2 written in base 3 are zero-free. %C A119909 No more terms < 3^20. - _Joshua Zucker_, Jun 05 2006 %e A119909 n: 1, 2, 4, 5, 7, 22, 43, 131, 394 %e A119909 n^2: 1, 4, 16, 25, 49, 484, 1849, 17161, 155236 %e A119909 n written in base 3: 1, 2, 11, 12, 21, 211, 1121, 11212, 112121 %e A119909 n^2 written in base 3: 1,11,121,221,1211,122221,2112111,212112121,21212221111 %t A119909 Select[Range[500],DigitCount[#,3,0]==DigitCount[#^2,3,0]==0&] (* _Harvey P. Dale_, Feb 06 2015 *) %o A119909 (PARI) isok(n) = vecmin(digits(n, 3)) && vecmin(digits(n^2, 3)); \\ _Michel Marcus_, Oct 10 2013 %Y A119909 Subsequence of A032924. %K A119909 base,more,nonn %O A119909 1,2 %A A119909 _Zak Seidov_, May 28 2006