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.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 56 |
| 4 | 220 |
| 5 | 857 |
| 6 | 3403 |
| 7 | 13535 |
| 8 | 54077 |
| 9 | 215900 |
| 10 | 862954 |
| 11 | 3450545 |
| 12 | 13802279 |
| 13 | 55201838 |
| 14 | 220792018 |
| 15 | 883134861 |
| 16 | 3532518195 |
| 17 | 14129951284 |
| 18 | 56519699688 |
| 19 | 226078355122 |
| 20 | 904312961284 |
| 21 | 3617249936000 |
| 22 | 14468996179294 |
| 23 | 57875977567596 |
| 24 | 231503907383054 |
| 25 | 926015589350438 |