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A015641 as a simple table

na(n)
20
30
40
50
61
76
821
956
10125
11251
12456
13786
141266
151980
162946
174311
186056
198436
2011370
2115231
2219866
2325851
2432801
2541655
2651786
2764366
2878601
2996151
30115495
31139246
32165286
33196541
34230681
35271585
36315256
37367616
38423461
39489011

[0,0,0,0,1,6,21,56,125,251,456,786,1266,1980,2946,
 4311,6056,8436,11370,15231,19866,25851,32801,
 41655,51786,64366,78601,96151,115495,139246,
 165286,196541,230681,271585,315256,367616,423461,
 489011]