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 | 0 |
| 2 | 0 |
| 3 | 12 |
| 4 | 224 |
| 5 | 2096 |
| 6 | 17732 |
| 7 | 160624 |
| 8 | 1498176 |
| 9 | 13404068 |
| 10 | 115123856 |
| 11 | 980282312 |
| 12 | 8327179132 |
| 13 | 70264899456 |
| 14 | 587727020332 |
| 15 | 4882463109244 |
| 16 | 40378339971868 |
| 17 | 332612594766452 |
| 18 | 2729309532474820 |
| 19 | 22316919930250328 |
| 20 | 181922495487675520 |
| 21 | 1479018078159317720 |