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A137110 Numbers k such that k and k^2 use only the digits 2, 5, 6 and 7. 5
5, 25, 26, 75, 76, 275, 525, 526, 725, 7525, 27525, 72576, 256266, 276725, 725725, 276726675, 756652275 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Generated with DrScheme.

If it exists, a(18) > 10^34. - David A. Corneth and Michael S. Branicky, May 25 2021

LINKS

Table of n, a(n) for n=1..17.

David A. Corneth, PARI program

Jonathan Wellons, Tables of Shared Digits

EXAMPLE

276726675^2 = 76577652656555625.

PROG

(Python)

def auptod(maxdigits, only="2567"):

  aset, digset, valid = set(), set(only), set(only)

  for e in range(1, maxdigits+1):

    newvalid = set()

    for tstr in valid:

      t = int(tstr)

      if set(str(t**2)) <= digset: aset.add(t)

      for d in digset:

        dtstr = d + tstr

        dt = int(dtstr)

        remstr = str(dt**2)[-e-1:]

        if set(remstr) <= digset: newvalid.add(dtstr)

    valid = newvalid

  return sorted(aset)

print(auptod(16)) # Michael S. Branicky, May 25 2021

(PARI) See PARI-link \\ David A. Corneth, May 25 2021

CROSSREFS

Sequence in context: A070381 A136912 A137111 * A036137 A070380 A068574

Adjacent sequences:  A137107 A137108 A137109 * A137111 A137112 A137113

KEYWORD

base,nonn,more

AUTHOR

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

STATUS

approved

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Last modified October 24 04:41 EDT 2021. Contains 348217 sequences. (Running on oeis4.)