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A001756 as a simple table

na(n)
315
460
5450
64500
755125
8793800
913097700
10243243000
115016886875
12113716102500
132808787731750
1475071235739500
152158298027510625
1666409170077250000
172177272076104125000
1875769068248423550000
192789248824895091934375
20108288483790044745687500

[15,60,450,4500,55125,793800,13097700,243243000,
 5016886875,113716102500,2808787731750,
 75071235739500,2158298027510625,66409170077250000,
 2177272076104125000,75769068248423550000,
 2789248824895091934375,108288483790044745687500]