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 | 0 |
| 2 | 4 |
| 3 | 8 |
| 4 | 36 |
| 5 | 120 |
| 6 | 456 |
| 7 | 1680 |
| 8 | 6340 |
| 9 | 23960 |
| 10 | 91224 |
| 11 | 348656 |
| 12 | 1337896 |
| 13 | 5149872 |
| 14 | 19877904 |
| 15 | 76907808 |
| 16 | 298176516 |
| 17 | 1158168792 |
| 18 | 4505865144 |
| 19 | 17555689008 |
| 20 | 68490100536 |
| 21 | 267518448912 |
| 22 | 1046041377264 |
| 23 | 4094231982048 |
| 24 | 16039426479336 |
| 25 | 62887835652720 |
| 26 | 246761907761776 |
| 27 | 968943740083040 |