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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 15 |
| 3 | 43 |
| 4 | 144 |
| 5 | 473 |
| 6 | 1529 |
| 7 | 5004 |
| 8 | 16335 |
| 9 | 53283 |
| 10 | 173960 |
| 11 | 567801 |
| 12 | 1853249 |
| 13 | 6049204 |
| 14 | 19744783 |
| 15 | 64447643 |
| 16 | 210360128 |
| 17 | 686623961 |
| 18 | 2241169033 |
| 19 | 7315270172 |
| 20 | 23877346447 |
| 21 | 77936655891 |
| 22 | 254388502200 |
| 23 | 830334694009 |
| 24 | 2710247124433 |
| 25 | 8846359824580 |
[4,15,43,144,473,1529,5004,16335,53283,173960, 567801,1853249,6049204,19744783,64447643, 210360128,686623961,2241169033,7315270172, 23877346447,77936655891,254388502200,830334694009, 2710247124433,8846359824580] |