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A199347 as a simple table

na(n)
13
27
337
443
547
673
7337
8347
9373
10433
11443
12733
13743
14773
153343
163347
173373
183433
193733
204337
214373
224447
234733
247333
257433
267477
2733343
2833347
2933377
3033773
3134337
3234747
3337337
3437447
3537747
3643777
3744773
3844777
3947737
4047743
4147777
4273433
4373477
4474377
4574747
4677347
4777377
4877447
4977477
5077743

[3,7,37,43,47,73,337,347,373,433,443,733,743,773,
 3343,3347,3373,3433,3733,4337,4373,4447,4733,7333,
 7433,7477,33343,33347,33377,33773,34337,34747,
 37337,37447,37747,43777,44773,44777,47737,47743,
 47777,73433,73477,74377,74747,77347,77377,77447,
 77477,77743]