A137019 Numbers k such that k and k^2 use only the digits 1, 2, 7 and 9.

1, 11, 27, 2777

Offset

1,2

Comments

Generated with DrScheme.

No further terms up to 9999999999. - Harvey P. Dale, Oct 13 2020

a(5) > 10^15 if it exists. - Chai Wah Wu, May 25 2021

Links

Table of n, a(n) for n=1..4.

Jonathan Wellons, Tables of Shared Digits [archived]

Example

2777^2 = 7711729, so 2777 is a term.

Mathematica

With[{c={1, 2, 7, 9}}, Select[FromDigits/@Flatten[Table[Tuples[c, n], {n, 4}], 1], SubsetQ[ c, IntegerDigits[#^2]]&]] (* Harvey P. Dale, Oct 13 2020 *)

Prog

(Python)
from itertools import product
A137019_list = [n for n in (int(''.join(d)) for l in range(1, 9) for d in product('1279', repeat=l)) if set(str(n**2)) <= set('1279')] # Chai Wah Wu, May 25 2021

Crossrefs

Sequence in context: A212776 A376144 A362528 * A122929 A030756 A065006

Adjacent sequences: A137016 A137017 A137018 * A137020 A137021 A137022

Keyword

base,nonn,more

Author

Jonathan Wellons (wellons(AT)gmail.com), Jan 22 2008

Status

approved