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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 10 |
| 3 | 26 |
| 4 | 72 |
| 5 | 174 |
| 6 | 597 |
| 7 | 1187 |
| 8 | 3115 |
| 9 | 7269 |
| 10 | 16520 |
| 11 | 39181 |
| 12 | 89951 |
| 13 | 210684 |
| 14 | 483773 |
| 15 | 1131924 |
| 16 | 2616441 |
| 17 | 6047969 |
| 18 | 14112456 |
| 19 | 32543109 |
| 20 | 75591535 |
| 21 | 175328537 |
| 22 | 405822918 |
| 23 | 941534652 |
| 24 | 2181820138 |
| 25 | 5057085795 |
| 26 | 11720944941 |
| 27 | 27171466826 |
| 28 | 62973901722 |
[4,10,26,72,174,597,1187,3115,7269,16520,39181, 89951,210684,483773,1131924,2616441,6047969, 14112456,32543109,75591535,175328537,405822918, 941534652,2181820138,5057085795,11720944941, 27171466826,62973901722] |