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 | 2 |
| 2 | 4 |
| 3 | 8 |
| 4 | 40 |
| 5 | 152 |
| 6 | 1128 |
| 7 | 6200 |
| 8 | 61120 |
| 9 | 442552 |
| 10 | 5466320 |
| 11 | 49399320 |
| 12 | 735847800 |
| 13 | 8003532512 |
| 14 | 139910204080 |
| 15 | 1784040237288 |
| 16 | 35858685086352 |
| 17 | 525504809786112 |
| 18 | 11953187179149408 |
| 19 | 198213959637435608 |
| 20 | 5037776918810353960 |