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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 16 |
| 3 | 72 |
| 4 | 142 |
| 5 | 332 |
| 6 | 668 |
| 7 | 1356 |
| 8 | 2634 |
| 9 | 5046 |
| 10 | 9480 |
| 11 | 17594 |
| 12 | 32286 |
| 13 | 58730 |
| 14 | 106028 |
| 15 | 190204 |
| 16 | 339322 |
| 17 | 602416 |
| 18 | 1064888 |
| 19 | 1875104 |
| 20 | 3290166 |
| 21 | 5754586 |
| 22 | 10035236 |
| 23 | 17452462 |
| 24 | 30275242 |
| 25 | 52395822 |
[4,16,72,142,332,668,1356,2634,5046,9480,17594, 32286,58730,106028,190204,339322,602416,1064888, 1875104,3290166,5754586,10035236,17452462, 30275242,52395822] |