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 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 56 |
| 5 | 440 |
| 6 | 4164 |
| 7 | 46046 |
| 8 | 582336 |
| 9 | 8288136 |
| 10 | 131090880 |
| 11 | 2280970032 |
| 12 | 43298796672 |
| 13 | 890441326320 |
| 14 | 19720847692896 |
| 15 | 467964024901200 |
| 16 | 11844861486802944 |
| 17 | 318549937907204352 |
| 18 | 9070876711252816128 |
| 19 | 272648086802525651328 |
| 20 | 8626452694650322744320 |