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A351470 Numbers m such that the largest digit in the decimal expansion of 1/m is 4.

%I A351470 #17 Feb 14 2022 13:17:42
%S A351470 25,225,250,693,2250,2439,2475,2500,3285,4095,4125,6930,6993,22500,
%T A351470 22725,23125,23245,24390,24750,24975,25000,30825,32850,40950,41250,
%U A351470 41625,42735,69300,69375,69735,69930,71225,225000,225225,227250,231250,232450,238095,243309,243900,247500,249750
%N A351470 Numbers m such that the largest digit in the decimal expansion of 1/m is 4.
%C A351470 If k is a term, 10*k is also a term.
%C A351470 First few primitive terms are 25, 225, 693, 2439, 2475, 3285, 4095, 4125, ...
%C A351470 There is no prime up to 2.6*10^8 (see comments in A333237).
%H A351470 <a href="/index/1#1overn">Index entries for sequences related to decimal expansion of 1/n</a>.
%e A351470 As 1/25 = 0.04, and 25 is the smallest number m such that the largest digit in the decimal expansion of 1/m is 4, so a(1) = 25.
%e A351470 As 1/693 = 0.001443001443001443..., so 693 is a term.
%t A351470 f[n_] := Union[ Flatten[ RealDigits[ 1/n][[1]] ]];Select[Range@1500000, Max@ f@# == 4 &]
%o A351470 (Python)
%o A351470 from itertools import count, islice
%o A351470 from sympy import n_order, multiplicity
%o A351470 def A351470_gen(startvalue=1): # generator of terms >= startvalue
%o A351470     for m in count(max(startvalue, 1)):
%o A351470         m2, m5 = multiplicity(2, m), multiplicity(5, m)
%o A351470         if max(str(10**(max(m2, m5)+n_order(10, m//2**m2//5**m5))//m)) == '4':
%o A351470             yield m
%o A351470 A351470_list = list(islice(A351470_gen(), 10)) # _Chai Wah Wu_, Feb 14 2022
%Y A351470 Cf. A333236.
%Y A351470 Similar with largest digit k: A333402 (k=1), A341383 (k=2), A350814 (k=3), this sequence (k=4), A351471 (k=5), A351472 (k=6), A351473 (k=7), A351474 (k=8), A333237 (k=9).
%K A351470 base,nonn
%O A351470 1,1
%A A351470 _Bernard Schott_ and _Robert G. Wilson v_, Feb 12 2022