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 A048409 #5 Oct 10 2019 23:17:49 %S A048409 0,1,2,3,4,5,6,7,8,9,18,29,70,81,92,181,292,707,818,929,1818,2929, %T A048409 7070,8181,9292,18181,29292,70707,81818,92929,181818,292929,707070, %U A048409 818181,929292,1818181,2929292,7070707,8181818,9292929,18181818,29292929 %N A048409 Numbers whose consecutive digits differ by 7. %Y A048409 Cf. A033075, A033088, A033081, A048407-A048410. %K A048409 nonn,base %O A048409 0,3 %A A048409 _Patrick De Geest_, Apr 15 1999