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 | 2 |
| 1 | 18 |
| 2 | 108 |
| 3 | 540 |
| 4 | 2430 |
| 5 | 10206 |
| 6 | 40824 |
| 7 | 157464 |
| 8 | 590490 |
| 9 | 2165130 |
| 10 | 7794468 |
| 11 | 27634932 |
| 12 | 96722262 |
| 13 | 334807830 |
| 14 | 1147912560 |
| 15 | 3902902704 |
| 16 | 13172296626 |
| 17 | 44165935746 |
| 18 | 147219785820 |
| 19 | 488149816140 |
| 20 | 1610894393262 |
| 21 | 5292938720718 |
| 22 | 17322344904168 |
| 23 | 56485907296200 |
| 24 | 183579198712650 |
| 25 | 594796603828986 |