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 | 4 |
| 3 | 12 |
| 4 | 42 |
| 5 | 120 |
| 6 | 415 |
| 7 | 1253 |
| 8 | 4078 |
| 9 | 12771 |
| 10 | 40518 |
| 11 | 126632 |
| 12 | 397349 |
| 13 | 1236040 |
| 14 | 3841920 |
| 15 | 11889451 |
| 16 | 36715750 |
| 17 | 113045937 |
| 18 | 347354344 |
| 19 | 1064918707 |
| 20 | 3258926926 |
| 21 | 9955461682 |
| 22 | 30365091843 |
| 23 | 92481086124 |
| 24 | 281292738961 |
| 25 | 854535966415 |
| 26 | 2593061420285 |
| 27 | 7860317530140 |
| 28 | 23803789290534 |