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 | 12 |
| 3 | 90 |
| 4 | 528 |
| 5 | 2850 |
| 6 | 14832 |
| 7 | 75810 |
| 8 | 383808 |
| 9 | 1932930 |
| 10 | 9705552 |
| 11 | 48648930 |
| 12 | 243605088 |
| 13 | 1219100610 |
| 14 | 6098716272 |
| 15 | 30503196450 |
| 16 | 152544778368 |
| 17 | 762810181890 |
| 18 | 3814309582992 |
| 19 | 19072323542370 |
| 20 | 95363943807648 |
| 21 | 476826695752770 |
| 22 | 2384154405761712 |
| 23 | 11920834803510690 |
| 24 | 59604362329076928 |
| 25 | 298022376554789250 |