A249915 - OEIS

A249915

Numbers k such that the decimal expansions of both k and k^2 have 2 as smallest digit and 6 as largest digit.

255465, 652244, 665256, 2534665, 2536656, 2554262, 6523462, 6524235, 6652242, 23352656, 23354365, 23523462, 23546665, 23565325, 25346665, 25425256, 25624665, 25625465, 65226242, 65234535, 235442656, 254234662, 255465525, 255645525, 256246665, 256254665

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OFFSET

1,1

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..2000 (n = 1..42 from Robert Israel).

MAPLE

M:= 10:

B:= [[2], [3], [4], [5], [6]]:

A:= NULL:

for d from 2 to M do

B:= map(b -> seq([op(b), i], i=2..6), B);

C:= select(b -> max(b)=6 and min(b) = 2, B);

X:= map(b -> add(b[i]*10^(d-i), i=1..d), C);

X:= select(proc(x) local L; L:= convert(x^2, base, 10); max(L) = 6 and min(L) = 2 end proc, X);

A:= A, op(X);

od:

A; # Robert Israel, Apr 27 2015

MATHEMATICA

fQ[n_] := Block[{d = DigitCount@ n}, Plus @@ Prepend[Take[d, -4], First@ d] == 0 && d[[2]] > 0 && d[[6]] > 0]; Select[Range@ 2600000, fQ@ # && fQ[#^2] &] (* Michael De Vlieger, Apr 27 2015 *)

PROG

(PARI) is(n) = vecmin(digits(n))==2 && vecmin(digits(n^2))==2 && vecmax(digits(n))==6 && vecmax(digits(n^2))==6

(Python)

from itertools import product

A249915_list = []

for l in range(10):

for a in product('23456', repeat = l):

for b in ('2', '4', '5', '6'):

s = ''.join(a)+b

if '2' in s and '6' in s:

n = int(s)

if {'2', '6'} <= set(str(n**2)) <= {'2', '3', '4', '5', '6'}: