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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 6 |
| 3 | 222 |
| 4 | 9918 |
| 5 | 486924 |
| 6 | 25267236 |
| 7 | 1359631776 |
| 8 | 75059524392 |
| 9 | 4223303759148 |
| 10 | 241144782230124 |
| 11 | 13930829740017132 |
| 12 | 812470444305924300 |
| 13 | 47760356825349969600 |
| 14 | 2826309951801018736800 |
| 15 | 168207011284961649886800 |
| 16 | 10060178088232285063542768 |
| 17 | 604273284101165691102038556 |
[1,6,222,9918,486924,25267236,1359631776, 75059524392,4223303759148,241144782230124, 13930829740017132,812470444305924300, 47760356825349969600,2826309951801018736800, 168207011284961649886800, 10060178088232285063542768, 604273284101165691102038556] |