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A027855 as a simple table

na(n)
12
23
34
45
56
67
78
89
910
1011
1113
1214
1315
1416
1517
1618
1719
1820
1921
2022
2123
2225
2326
2427
2528
2629
2731
2832
2933
3034
3135
3237
3338
3439
3541
3642
3743
3844
3946
4047
4149
4250
4351
4452
4553
4654
4755
4857
4958
5059
5161
5262
5364
5465
5566
5667
5768
5869
5971
6073
6174
6275
6376
6477
6578
6679
6781
6882
6983
7085
7186
7287

[2,3,4,5,6,7,8,9,10,11,13,14,15,16,17,18,19,20,21,
 22,23,25,26,27,28,29,31,32,33,34,35,37,38,39,41,
 42,43,44,46,47,49,50,51,52,53,54,55,57,58,59,61,
 62,64,65,66,67,68,69,71,73,74,75,76,77,78,79,81,
 82,83,85,86,87]