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| n | a(n) |
|---|---|
| 2 | 4 |
| 3 | 12 |
| 4 | 52 |
| 5 | 172 |
| 6 | 580 |
| 7 | 1852 |
| 8 | 5828 |
| 9 | 17980 |
| 10 | 54788 |
| 11 | 165116 |
| 12 | 493316 |
| 13 | 1463036 |
| 14 | 4312068 |
| 15 | 12641276 |
| 16 | 36887556 |
| 17 | 107201532 |
| 18 | 310427652 |
| 19 | 896045052 |
| 20 | 2579017732 |
| 21 | 7403843580 |
| 22 | 21205303300 |
| 23 | 60604891132 |
| 24 | 172872744964 |
| 25 | 492233179132 |
| 26 | 1399272374276 |
[4,12,52,172,580,1852,5828,17980,54788,165116, 493316,1463036,4312068,12641276,36887556, 107201532,310427652,896045052,2579017732, 7403843580,21205303300,60604891132,172872744964, 492233179132,1399272374276] |