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 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 12 |
| 5 | 33 |
| 6 | 90 |
| 7 | 252 |
| 8 | 729 |
| 9 | 2160 |
| 10 | 6480 |
| 11 | 19521 |
| 12 | 58806 |
| 13 | 176904 |
| 14 | 531441 |
| 15 | 1595052 |
| 16 | 4785156 |
| 17 | 14353281 |
| 18 | 43053282 |
| 19 | 129146724 |
| 20 | 387420489 |
| 21 | 1162241784 |
| 22 | 3486725352 |
| 23 | 10460235105 |
| 24 | 31380882462 |
| 25 | 94143001680 |
| 26 | 282429536481 |
| 27 | 847289140884 |