%I #25 Oct 02 2017 00:57:24

%S 6734,67434,577734,667334,745356,6674334,6734744,6756734,7373376,

%T 7453574,7466434,7533576,66673334,67345644,67656734,74547734,74656376,

%U 75733576,666743334,667335356,746556344,5775434474,6666733334,6666733576,6676476434,7447533576

%N Numbers n such that the decimal expansions of both n and n^2 have 3 as smallest digit and 7 as largest digit.

%H Chai Wah Wu, <a href="/A257486/b257486.txt">Table of n, a(n) for n = 1..1000</a> (n = 71..178 from Giovanni Resta)

%t fQ[n_] := Block[{d = DigitCount@ n}, Plus @@ Join[Take[d, {1, 2}], Take[d, {8, 10}]] == 0 && d[[3]] > 0 && d[[7]] > 0]; Select[Range@ 1000000, fQ@# && fQ[#^2] &] (* _Michael De Vlieger_, Apr 27 2015 *)

%o (PARI) is(n) = vecmin(digits(n))==3 && vecmin(digits(n^2))==3 && vecmax(digits(n))==7 && vecmax(digits(n^2))==7

%o (Python)

%o from itertools import product, repeat

%o A257486_list = []

%o for l in range(12):

%o ....for a in product('34567',repeat = l):

%o ........for b in ('4','5','6'):

%o ............s = ''.join(a)+b

%o ............if '3' in s and '7' in s:

%o ................n = int(s)

%o ................if {'3','7'} <= set(str(n**2)) <= {'3','4','5','6','7'}:

%o ....................A257486_list.append(n) # _Chai Wah Wu_, May 02 2015

%Y Cf. A137121, A256630, A256631, A256633, A256634, A256708, A256709, A256889, A257197, A257210, A257211, A256601, A257310, A249915, A257123, A257368, A257485.

%K nonn,base

%O 1,1

%A _Felix Fröhlich_, Apr 26 2015

%E a(22)-a(26) from _Hiroaki Yamanouchi_, May 03 2015 (using _Chai Wah Wu_'s b-file)