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 | 4 |
| 2 | 24 |
| 3 | 156 |
| 4 | 1120 |
| 5 | 8740 |
| 6 | 73384 |
| 7 | 657900 |
| 8 | 6259184 |
| 9 | 62876852 |
| 10 | 664134968 |
| 11 | 7349666684 |
| 12 | 84956020864 |
| 13 | 1023006054980 |
| 14 | 12802727760840 |
| 15 | 166174971580684 |
| 16 | 2232866214809360 |
| 17 | 31007771007956948 |
| 18 | 444360490882720344 |
| 19 | 6562410784684023452 |
| 20 | 99749853821538893216 |
| 21 | 1558780425524233360740 |