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 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 44 |
| 5 | 152 |
| 6 | 524 |
| 7 | 1803 |
| 8 | 6204 |
| 9 | 21351 |
| 10 | 73480 |
| 11 | 252880 |
| 12 | 870280 |
| 13 | 2995049 |
| 14 | 10307396 |
| 15 | 35472677 |
| 16 | 122078436 |
| 17 | 420130248 |
| 18 | 1445868996 |
| 19 | 4975926307 |
| 20 | 17124540796 |
| 21 | 58933729999 |
| 22 | 202819133840 |
| 23 | 697997582240 |
| 24 | 2402143306640 |
| 25 | 8266923285201 |
| 26 | 28450434416004 |
| 27 | 97911543452733 |