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 | 0 |
| 1 | 4 |
| 2 | 20 |
| 3 | 102 |
| 4 | 520 |
| 5 | 2570 |
| 6 | 12300 |
| 7 | 57358 |
| 8 | 262160 |
| 9 | 1179666 |
| 10 | 5242900 |
| 11 | 23068694 |
| 12 | 100663320 |
| 13 | 436207642 |
| 14 | 1879048220 |
| 15 | 8053063710 |
| 16 | 34359738400 |
| 17 | 146028888098 |
| 18 | 618475290660 |
| 19 | 2611340116006 |
| 20 | 10995116277800 |
| 21 | 46179488366634 |
| 22 | 193514046488620 |
| 23 | 809240558043182 |
| 24 | 3377699720527920 |