
EXAMPLE

The table reads:
n \ k's
0 : 0, 1, 2, 3, 6, 7, 10, 11, 19, 35 (= A030703)
1 : 4, 5, 8, 12, 14, 15, 18, 27, 43, 47, 51
2 : 9, 16, 17, 20, 24, 26, 28, 29, 34, 38, 52, 93
3 : 13, 21, 22, 23, 30, 31, 36, 37, 42, 44, 46, 49, 58
4 : 25, 32, 33, 50, 53, 54, 59, 66, 122
5 : 55, 56, 57, 61, 62, 64, 67, 72, 73, 74
...
Column 0 is A063606: least k such that 7^k has n digits '0' in base 10.
Row lengths are 10, 11, 12, 13, 9, 10, 9, 7, 10, 14, 21, 10, 18, 7, 11, 11, 12, 15, 17, 10, ... (not in OEIS).
Last term of the rows are (35, 51, 93, 58, 122, 74, 108, 131, 118, 152, 195, 192, 236, 184, 247, 243, 254, 286, 325, 292, ...), not in OEIS.
The inverse permutation is (0, 1, 2, 3, 10, 11, 4, 5, 12, 21, 6, 7, 13, 33, 14, 15, 22, 23, 16, 8, 24, 34, 35, 36, 25, 46, 26, 17, 27, 28, 37, ...), not in OEIS.
Number of '0's in 7^n = row number of n: (0, 0, 0, 0, 1, 1, 0, 0, 1, 2, 0, 0, 1, 3, 1, 1, 2, 2, 1, 0, 2, 3, 3, 3, 2, 4, 2, 1, 2, 2, 3, 3, 4, 4, ...), not in OEIS.
Number of '0's in 7^n = row number of n: (0, 0, 0, 0, 1, 1, 0, 0, 1, 2, 0, 0, 1, 3, 1, 1, 2, 2, 1, 0, 2, 3, 3, 3, 2, 4, 2, 1, 2, 2, 3, 3, 4, 4, ...), not in OEIS.
