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Numbers n such that the decimal expansions of both n and n^2 have 0 as smallest digit and 8 as largest digit.
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%I #14 Oct 19 2021 17:46:36

%S 280,508,780,805,1028,1078,1280,1308,1680,1780,1805,1840,2078,2608,

%T 2680,2780,2800,2801,2802,2805,2840,2850,3280,3580,3780,3805,3808,

%U 3850,4048,4078,4280,4780,4804,4805,4880,5008,5018,5028,5048,5078,5080,5084,5180,5280

%N Numbers n such that the decimal expansions of both n and n^2 have 0 as smallest digit and 8 as largest digit.

%H Felix Fröhlich, <a href="/A256708/b256708.txt">Table of n, a(n) for n = 1..10000</a>

%t fQ[n_] := Block[{c = DigitCount@ n}, And[c[[9]] == 0, c[[8]] > 0, c[[10]] > 0]]; Select[Range@ 5280, fQ@ # && fQ[#^2] &] (* _Michael De Vlieger_, Apr 12 2015 *)

%t maxdQ[n_]:=Module[{id1=IntegerDigits[n],id2=IntegerDigits[n^2]},Max[ id1] == Max[ id2] == 8&&Min[id1]==Min[id2]==0]; Select[Range[6000],maxdQ] (* _Harvey P. Dale_, Oct 19 2021 *)

%o (PARI) is(n) = vecmin(digits(n))==0 && vecmin(digits(n^2))==0 && vecmax(digits(n))==8 && vecmax(digits(n^2))==8

%Y Cf. A136814, A136820, A136825, A136829, A136832, A136840, A136845, A136849, A136904, A256630, A256631, A256633, A256634, A256709.

%K nonn,base

%O 1,1

%A _Felix Fröhlich_, Apr 08 2015