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 | 1 |
| 3 | 3 |
| 4 | 11 |
| 5 | 39 |
| 6 | 140 |
| 7 | 504 |
| 8 | 1823 |
| 9 | 6621 |
| 10 | 24144 |
| 11 | 88380 |
| 12 | 324699 |
| 13 | 1197045 |
| 14 | 4427565 |
| 15 | 16427385 |
| 16 | 61129025 |
| 17 | 228103185 |
| 18 | 853399640 |
| 19 | 3200710680 |
| 20 | 12032399045 |
| 21 | 45332769075 |
| 22 | 171148151095 |
| 23 | 647412581643 |
| 24 | 2453529142471 |
| 25 | 9314461044639 |
| 26 | 35419207688050 |
| 27 | 134894888442714 |
| 28 | 514506926871927 |