A256709 - OEIS

A256709

Numbers n such that the decimal expansions of both n and n^2 have 0 as smallest digit and 9 as largest digit.

%I #11 Apr 23 2015 13:37:37

%S 509,890,903,905,930,950,960,970,980,990,1039,1091,1095,1097,1390,

%T 1709,1903,1905,1930,1970,1980,1990,2049,2093,2095,2097,2190,2509,

%U 2809,2903,2905,2907,2930,2970,2990,3009,3049,3079,3090,3092,3095,3097,3098,3099,3209

%N Numbers n such that the decimal expansions of both n and n^2 have 0 as smallest digit and 9 as largest digit.

%H Felix Fröhlich, <a href="/A256709/b256709.txt">Table of n, a(n) for n = 1..10000</a>

%t fQ[n_] := Block[{c = DigitCount@ n}, And[c[[9]] > 0, c[[10]] > 0]]; Select[Range@ 3209, fQ@ # && fQ[#^2] &] (* _Michael De Vlieger_, Apr 12 2015 *)

%o (PARI) is(n) = vecmin(digits(n))==0 && vecmin(digits(n^2))==0 && vecmax(digits(n))==9 && vecmax(digits(n^2))==9

%Y Cf. A136836, A256630, A256631, A256633, A256634, A256708.

%K nonn,base

%O 1,1

%A _Felix Fröhlich_, Apr 08 2015