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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 11 |
| 4 | 28 |
| 5 | 68 |
| 6 | 169 |
| 7 | 470 |
| 8 | 1276 |
| 9 | 3395 |
| 10 | 9016 |
| 11 | 26240 |
| 12 | 74017 |
| 13 | 204590 |
| 14 | 568120 |
| 15 | 1659350 |
| 16 | 4770820 |
| 17 | 13538480 |
| 18 | 38435515 |
| 19 | 113673998 |
| 20 | 331360936 |
| 21 | 955040204 |
| 22 | 2757123412 |
| 23 | 8185543376 |
| 24 | 24071728150 |
| 25 | 70215321944 |
| 26 | 204746123776 |
| 27 | 612178795262 |
| 28 | 1813222985320 |
[2,4,11,28,68,169,470,1276,3395,9016,26240,74017, 204590,568120,1659350,4770820,13538480,38435515, 113673998,331360936,955040204,2757123412, 8185543376,24071728150,70215321944,204746123776, 612178795262,1813222985320] |