A053332 - OEIS

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A053332 as a simple table

n	a(n)
1	4
2	44
3	744
4	7744
5	47744
6	447744
7	4447744
8	44447744
9	444447744
10	4444447744
11	74444447744
12	474444447744
13	4474444447744
14	44474444447744
15	444474444447744
16	7444474444447744
17	77444474444447744
18	477444474444447744

[4,44,744,7744,47744,447744,4447744,44447744, 444447744,4444447744,74444447744,474444447744, 4474444447744,44474444447744,444474444447744, 7444474444447744,77444474444447744, 477444474444447744]