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A249915
Numbers k such that the decimal expansions of both k and k^2 have 2 as smallest digit and 6 as largest digit.
10
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
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'}:
A249915_list.append(n) # Chai Wah Wu, Apr 29 2015
KEYWORD
nonn,base
AUTHOR
Felix Fröhlich, Apr 21 2015
STATUS
approved