A305928 Irregular table: row n >= 0 lists all k >= 0 such that the decimal representation of 8^k has n digits '0' (conjectured).

0, 1, 2, 3, 5, 6, 8, 9, 11, 12, 13, 17, 24, 27, 4, 7, 10, 15, 16, 19, 22, 25, 28, 32, 43, 14, 18, 20, 21, 26, 36, 37, 39, 45, 47, 49, 50, 55, 57, 77, 23, 29, 30, 31, 38, 41, 44, 51, 52, 58, 61, 42, 53, 59, 62, 65, 69, 33, 40, 48, 56, 60, 64, 73, 76, 80, 86, 114, 119, 35, 46

Offset: 0

Author

M. F. Hasler, Jun 19 2018

Keywords

• nonn
• base
• tabf

Comments

The set of (nonempty) rows forms a partition of the nonnegative integers.

Read as a flattened sequence, a permutation of the nonnegative integers.

In the same way, another choice of (basis, digit, base) = (m, d, b) different from (8, 0, 10) will yield a similar partition of the nonnegative integers, trivial if m is a multiple of b.

It remains an open problem to provide a proof that the rows are complete, in the same way as each of the terms of A020665 is unproved.

We can also decide that the rows are to be truncated as soon as no term is found within a sufficiently large search limit. (For all of the displayed rows, there is no additional term up to many orders of magnitude beyond the last term.) That way the rows are well-defined, but it is no longer guaranteed to have a partition of the integers.

Examples

			The table reads:
n \ k's
0 : 0, 1, 2, 3, 5, 6, 8, 9, 11, 12, 13, 17, 24, 27 (= A030704)
1 : 4, 7, 10, 15, 16, 19, 22, 25, 28, 32, 43
2 : 14, 18, 20, 21, 26, 36, 37, 39, 45, 47, 49, 50, 55, 57, 77
3 : 23, 29, 30, 31, 38, 41, 44, 51, 52, 58, 61
4 : 42, 53, 59, 62, 65, 69
5 : 33, 40, 48, 56, 60, 64, 73, 76, 80, 86, 114, 119
...
Column 0 is A063596: least k such that 8^k has n digits '0' in base 10.
Row lengths are 14, 11, 15, 11, 6, 12, 10, 7, 14, 21, 9, 9, 15, 8, 6, 10, 8, 13, ... (not in the OEIS).
The inverse permutation is (0, 1, 2, 3, 14, 4, 5, 15, 6, 7, 16, 8, 9, 10, 25, 17, 18, 11, 26, 19, 27, 28, 20, 40, 12, 21, 29, 13, 22, ...), also not in the OEIS.
		

Links

• M. F. Hasler, Zeroless powers.. OEIS Wiki, March 2014

Crossrefs

Cf. A030704, A063596.

Cf. A305932 (analog for 2^k), A305933 (analog for 3^k), A305924 (analog for 4^k), ..., A305929 (analog for 9^k).

Programs

Mathematica

mx = 1000; g[n_] := g[n] = DigitCount[8^n, 10, 0]; f[n_] := Select[Range@mx, g@# == n &]; Table[f@n, {n, 0, 4}] // Flatten (* Robert G. Wilson v, Jun 20 2018 *)

PARI

apply( A305928_row(n,M=50*(n+1))=select(k->#select(d->!d,digits(8^k))==n,[0..M]), [0..7])

Formula

Row n consists of integers in row n of A305932 divided by 3.