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 | 1 |
| 2 | -1 |
| 3 | 2 |
| 4 | -4 |
| 5 | 10 |
| 6 | -26 |
| 7 | 71 |
| 8 | -199 |
| 9 | 569 |
| 10 | -1652 |
| 11 | 4855 |
| 12 | -14413 |
| 13 | 43153 |
| 14 | -130143 |
| 15 | 394967 |
| 16 | -1205268 |
| 17 | 3695771 |
| 18 | -11381215 |
| 19 | 35183209 |
| 20 | -109138163 |
| 21 | 339599993 |
| 22 | -1059702401 |
| 23 | 3315256789 |
| 24 | -10396158911 |
| 25 | 32671424776 |
| 26 | -102879610571 |
| 27 | 324557399534 |
| 28 | -1025643986057 |
| 29 | 3246330348415 |
| 30 | -10290418283163 |