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 | 4 |
| 2 | 16 |
| 3 | 57 |
| 4 | 207 |
| 5 | 751 |
| 6 | 2720 |
| 7 | 9861 |
| 8 | 35741 |
| 9 | 129540 |
| 10 | 469528 |
| 11 | 1701805 |
| 12 | 6168220 |
| 13 | 22356839 |
| 14 | 81032722 |
| 15 | 293704534 |
| 16 | 1064537220 |
| 17 | 3858433620 |
| 18 | 13984959985 |
| 19 | 50688731051 |
| 20 | 183722188635 |
| 21 | 665904273716 |
| 22 | 2413581640617 |
| 23 | 8748068704189 |
| 24 | 31707527421628 |