A028028 - OEIS

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A028028 as a simple table

n	a(n)
0	1
1	21
2	286
3	3234
4	33187
5	322455
6	3035152
7	28040628
8	256229413
9	2326373049
10	21042916258
11	189930286182
12	1712158289479
13	15423616827003
14	138884571944404
15	1250325501927096
16	11254768340210185
17	101302177508279517

[1,21,286,3234,33187,322455,3035152,28040628, 256229413,2326373049,21042916258,189930286182, 1712158289479,15423616827003,138884571944404, 1250325501927096,11254768340210185, 101302177508279517]