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) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 9 |
| 4 | 120 |
| 5 | 1550 |
| 6 | 23310 |
| 7 | 411747 |
| 8 | 8388576 |
| 9 | 193710204 |
| 10 | 4999999950 |
| 11 | 142655835245 |
| 12 | 4458050224056 |
| 13 | 151437553296042 |
| 14 | 5556003412778910 |
| 15 | 218946945190429575 |
| 16 | 9223372036854775680 |
| 17 | 413620130943168381944 |
| 18 | 19673204037648268787550 |
| 19 | 989209827830156794561809 |
| 20 | 52428799999999999999999800 |