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A181393 as a simple table

na(n)
13
27
321
447
5329
6987
72207
8103729
9726103
102178309
114870847
1210610209857723
1323725150497407
1410749959329
15505248088463
163536736619241

[3,7,21,47,329,987,2207,103729,726103,2178309,
 4870847,10610209857723,23725150497407,10749959329,
 505248088463,3536736619241]