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.
sum(10**n) - _sum(10**(n-1)) # _David Radcliffe's wiki page.
sum(10**n) - _sum(10**(n-1)) # _David Radcliffe has authored 0 sequences.