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 | 5 |
| 2 | -15 |
| 3 | 85 |
| 4 | -415 |
| 5 | 2085 |
| 6 | -10415 |
| 7 | 52085 |
| 8 | -260415 |
| 9 | 1302085 |
| 10 | -6510415 |
| 11 | 32552085 |
| 12 | -162760415 |
| 13 | 813802085 |
| 14 | -4069010415 |
| 15 | 20345052085 |
| 16 | -101725260415 |
| 17 | 508626302085 |
| 18 | -2543131510415 |
| 19 | 12715657552085 |
| 20 | -63578287760415 |