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A002978 as a simple table

na(n)
10
20
34
40
512
68
748
896
9320
10888
112748
128384
1326340
1483568
15268864
16873648
172865216
189470784
1931525524
20105594912
21355673804
221204059144
234094727168
2413983145888
2547932777680
26164881688088
27568990371212
281969356192624
296834965581764
3023782468159920

[0,0,4,0,12,8,48,96,320,888,2748,8384,26340,83568,
 268864,873648,2865216,9470784,31525524,105594912,
 355673804,1204059144,4094727168,13983145888,
 47932777680,164881688088,568990371212,
 1969356192624,6834965581764,23782468159920]