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) |
|---|---|
| 1 | 0 |
| 2 | 5 |
| 3 | 20 |
| 4 | 123 |
| 5 | 680 |
| 6 | 4070 |
| 7 | 23565 |
| 8 | 138014 |
| 9 | 805249 |
| 10 | 4704141 |
| 11 | 27469522 |
| 12 | 160428571 |
| 13 | 936897912 |
| 14 | 5471539885 |
| 15 | 31953953498 |
| 16 | 186612354231 |
| 17 | 1089822896327 |
| 18 | 6364606387628 |
| 19 | 37169536347339 |
| 20 | 217071469820879 |
| 21 | 1267705419106309 |