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 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 52 |
| 5 | 372 |
| 6 | 3058 |
| 7 | 28074 |
| 8 | 282028 |
| 9 | 3059328 |
| 10 | 35497672 |
| 11 | 437499541 |
| 12 | 5696752234 |
| 13 | 78036803430 |
| 14 | 1120687989348 |
| 15 | 16823652188164 |
| 16 | 263345788211608 |
| 17 | 4289062071449610 |
| 18 | 72543038644585822 |
| 19 | 1271980596430351862 |
| 20 | 23085579883157411532 |
| 21 | 433071407705851089244 |