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 | 3 |
| 3 | 15 |
| 4 | 105 |
| 5 | 937 |
| 6 | 10059 |
| 7 | 124607 |
| 8 | 1720593 |
| 9 | 25578001 |
| 10 | 391041299 |
| 11 | 5628440015 |
| 12 | 55397475705 |
| 13 | -847789025159 |
| 14 | -93469767131685 |
| 15 | -5040670692970753 |
| 16 | -236210967512228575 |
| 17 | -10629917015586704351 |
| 18 | -475183316832486106589 |
| 19 | -21394016956935371375601 |
| 20 | -975459739630268065696887 |