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 | 3 |
| 2 | 18 |
| 3 | 90 |
| 4 | 270 |
| 5 | 1134 |
| 6 | 5670 |
| 7 | 2430 |
| 8 | 7290 |
| 9 | 133650 |
| 10 | 112266 |
| 11 | 1990170 |
| 12 | 9950850 |
| 13 | 2296350 |
| 14 | 984150 |
| 15 | 117113850 |
| 16 | 351341550 |
| 17 | 33657930 |
| 18 | 21597171750 |
| 19 | 3410079750 |
| 20 | 572893398 |
| 21 | 33613643250 |
| 22 | 834229509750 |
| 23 | 108812544750 |
| 24 | 544062723750 |
| 25 | 18280507518 |
| 26 | 105464466450 |
| 27 | 18690647109750 |