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 | 3 |
| 2 | 15 |
| 3 | 105 |
| 4 | 945 |
| 5 | 4158 |
| 6 | 75075 |
| 7 | 579150 |
| 8 | 34459425 |
| 9 | 339489150 |
| 10 | 16499172690 |
| 11 | 1724913508500 |
| 12 | 878428175625 |
| 13 | 131358797955000 |
| 14 | 252664626678750 |
| 15 | 3891675750482520 |
| 16 | 221643095476699771875 |
| 17 | 208605266331011550000 |
| 18 | 32498195069133543750 |
| 19 | 807994071847270157850000 |
| 20 | 125885476393804690593030 |