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 A018831 #15 Apr 05 2024 08:01:28 %S A018831 0,1,7,30,49,285,343,911,1900,2208,2401,13962,16807,59763,64098,69128, %T A018831 85880,97734,117649,195032,418341,754422,823543,2162126,2629229, %U A018831 2790841,3488518,3842400,4960401,5764801,7923812,8559490,15134882,19765943,31466333,36415297 %N A018831 Numbers n such that n is a substring of its square in base 7 (written in base 10). %t A018831 Select[Range[0, 10^7], StringContainsQ[IntegerString[#^2, 7], IntegerString[#, 7]] &] (* _Paolo Xausa_, Apr 05 2024 *) %Y A018831 Cf. A018826 (base 2), A018827 (base 3), A018828 (base 4), A018829 (base 5), A018830 (base 6), A018832 (base 8), A018833 (base 9), A018834 (base 10). %K A018831 nonn,base %O A018831 1,3 %A A018831 _David W. Wilson_ %E A018831 a(35)-a(36) from _Pontus von Brömssen_, Apr 04 2024