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 | 2 |
| 3 | 9 |
| 4 | 72 |
| 5 | 665 |
| 6 | 6960 |
| 7 | 85057 |
| 8 | 1199744 |
| 9 | 19070865 |
| 10 | 336372480 |
| 11 | 6522635801 |
| 12 | 137996694528 |
| 13 | 3163206890857 |
| 14 | 78085740701696 |
| 15 | 2065239729737745 |
| 16 | 58263449436979200 |
| 17 | 1746433243580269217 |
| 18 | 55428341343200280576 |
| 19 | 1856918215298125692073 |
| 20 | 65483209810866254643200 |
| 21 | 2424691204935999655757241 |