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A031978 as a simple table

na(n)
12
23
34
45
56
67
79
82
93
104
115
126
137
149
152
162
1722
1823
1924
2025
2126
2227
232
2429
253
263
2732
2833
2934
3035
3136
3237
333
3439
354
364
3742
3843
3944
4045
4146
4247
434
4449
455
465
4752
4853
4954
5055
5156
5257
535
5459
556
566
5762
5863
5964
6065
6166
6267
636
6469
657
667
6772
6873
6974
7075
7176
7277
737
7479
752
763
774
785
796
807
819
829
839

[2,3,4,5,6,7,9,2,3,4,5,6,7,9,2,2,22,23,24,25,26,
 27,2,29,3,3,32,33,34,35,36,37,3,39,4,4,42,43,44,
 45,46,47,4,49,5,5,52,53,54,55,56,57,5,59,6,6,62,
 63,64,65,66,67,6,69,7,7,72,73,74,75,76,77,7,79,2,
 3,4,5,6,7,9,9,9]