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A137119 Numbers k such that k and k^2 use only the digits 2, 6, 7 and 9. 0
26, 27, 277, 269777 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Generated with DrScheme.

No further terms up to 2*10^27. - Robert Israel, Oct 04 2019

LINKS

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

J. Wellons, Tables of Shared Digits

EXAMPLE

269777^2 = 72779629729.

MAPLE

Extend:= proc(x, d)

local i;

  op(select(t -> member(floor(t^2/10^(d)) mod 10, {2, 6, 7, 9}), [seq(i*10^d+x, i=[2, 6, 7, 9])]))

end proc:

R[0]:= {6, 7}:

for m from 1 to 10 do R[m]:= map(Extend, R[m-1], m) od:

{seq(op(select(t -> convert(convert(t^2, base, 10), set) subset {2, 6, 7, 9}, R[m])), m=0..10)}; # Robert Israel, Oct 04 2019

PROG

(MAGMA) [k:k in [1..10^6]| Set(Intseq(k)) join Set(Intseq(k^2)) subset {2, 6, 7, 9}]; // Marius A. Burtea, Oct 04 2019

(Python)

def test(n):

    while n > 0:

        d, n = n%10, n//10

        if d == 0 or d == 1 or d == 3 or d == 4 or d == 5 or d == 8:

            return 0

    return 1

n, a = 0, 1

while n >= 0:

    if test(a) and test(a*a):

        n = n+1

        print(n, a)

    a = a+1 # A.H.M. Smeets, Oct 05 2019

CROSSREFS

Sequence in context: A136923 A042394 A137118 * A042396 A042398 A042400

Adjacent sequences:  A137116 A137117 A137118 * A137120 A137121 A137122

KEYWORD

nonn,base,more

AUTHOR

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

STATUS

approved

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Last modified December 14 07:03 EST 2019. Contains 329978 sequences. (Running on oeis4.)