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 | 6 |
| 4 | 24 |
| 5 | 90 |
| 6 | 306 |
| 7 | 1008 |
| 8 | 3240 |
| 9 | 10266 |
| 10 | 32190 |
| 11 | 100188 |
| 12 | 310074 |
| 13 | 955500 |
| 14 | 2934288 |
| 15 | 8986086 |
| 16 | 27456840 |
| 17 | 83735370 |
| 18 | 254962062 |
| 19 | 775270908 |
| 20 | 2354646294 |
| 21 | 7144301016 |
| 22 | 21657653028 |
| 23 | 65603494458 |
| 24 | 198584527338 |
| 25 | 600758100540 |
| 26 | 1816426149876 |
| 27 | 5489387016378 |
| 28 | 16582071393240 |