A037767 - OEIS

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A037767 as a simple table

n	a(n)
1	3
2	18
3	110
4	661
5	3969
6	23814
7	142886
8	857317
9	5143905
10	30863430
11	185180582
12	1111083493
13	6666500961
14	39999005766
15	239994034598
16	1439964207589
17	8639785245537
18	51838711473222
19	311032268839334
20	1866193613036005

[3,18,110,661,3969,23814,142886,857317,5143905, 30863430,185180582,1111083493,6666500961, 39999005766,239994034598,1439964207589, 8639785245537,51838711473222,311032268839334, 1866193613036005]