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A321521 as a simple table

na(n)
11
21
37
421
5121
6715
75041
840293
9362887
103628681
1139916801
12479000895
136227020801
1487178286161
151307674368127
1620922789847653
17355687428096001
186402373705365835
19121645100408832001
202432902008173011101
2151090942171709445047
221124000727777567763201

[1,1,7,21,121,715,5041,40293,362887,3628681,
 39916801,479000895,6227020801,87178286161,
 1307674368127,20922789847653,355687428096001,
 6402373705365835,121645100408832001,
 2432902008173011101,51090942171709445047,
 1124000727777567763201]