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A136960
Numbers k such that k and k^2 use only the digits 0, 4, 7 and 9.
1
0, 7, 70, 97, 700, 970, 997, 7000, 9700, 9970, 9997, 70000, 97000, 99700, 99970, 99997, 700000, 970000, 997000, 999700, 999970, 999997, 7000000, 9700000, 9970000, 9997000, 9999700, 9999970, 9999997, 70000000, 97000000, 99700000, 99970000, 99997000, 99999700, 99999970, 99999997, 700000000, 970000000, 997000000, 999700000, 999970000
OFFSET
1,2
COMMENTS
Generated with DrScheme.
From Robert Israel, Jun 12 2019: (Start)
If k is in the sequence, then so is 10*k.
Includes 10^a - 3*10^b for b < a.
The rightmost nonzero digit of k must be 7; the leftmost digit must be 0, 7 or 9. (End)
LINKS
J. Wellons, Tables of Shared Digits [archived]
EXAMPLE
999999999999997^2 = 999999999999994000000000000009.
CROSSREFS
Sequence in context: A061476 A136959 A136952 * A003363 A069542 A063416
KEYWORD
base,nonn
AUTHOR
Jonathan Wellons (wellons(AT)gmail.com), Jan 22 2008
STATUS
approved