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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 70 |
| 4 | 555 |
| 5 | 2961 |
| 6 | 31108 |
| 7 | 213228 |
| 8 | 2799765 |
| 9 | 23455135 |
| 10 | 369569046 |
| 11 | 3659001138 |
| 12 | 67261566463 |
| 13 | 768390239085 |
| 14 | 16142775951240 |
| 15 | 209002145031256 |
| 16 | 4939689441079593 |
| 17 | 71478733600689723 |
| 18 | 1877081987610245530 |
| 19 | 30021068112289683870 |
| 20 | 867211878275933435091 |
| 21 | 15190660464818580038473 |
[1,3,18,70,555,2961,31108,213228,2799765,23455135, 369569046,3659001138,67261566463,768390239085, 16142775951240,209002145031256,4939689441079593, 71478733600689723,1877081987610245530, 30021068112289683870,867211878275933435091, 15190660464818580038473] |