%I #22 Apr 09 2024 14:18:51
%S 1,18,28,6,42,58,22,13,44,2,108,48,21,46,148,13,78,178,6,99,18,8,228,
%T 7,41,6,268,15,272,66,34,28,138,112,116,179,5,378,388,18,204,418,6,
%U 219,32,48,66,239,81,498,508,43,506,42,60,42,284,192,90,299,84,618,48,35
%N Number of digits in A128857(n).
%H A. V. Chupin, <a href="/A128858/b128858.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) = order of 10 (mod 10*n - 1). - _Arkadiusz Wesolowski_, Nov 17 2012
%t Give[a_,n_]:=Block[{d=Floor[Log[10,n]]+1,m=(10n-1)/GCD[10n-1,a]}, If[m?1,While[PowerMod[10,d,m]!=N,d++ ],d=1]; ((10^(d+1)-1) a n)/(10n-1)]; Length[IntegerDigits[Give[1,n]]]
%o (Python)
%o from sympy import n_order
%o def A128858(n): return n_order(10,10*n-1) # _Chai Wah Wu_, Apr 09 2024
%Y Cf. A128857.
%K nonn,base,changed
%O 1,2
%A Anton V. Chupin (chupin(X)icmm.ru), Apr 12 2007
%E a(10) = 2 corrected by _Gerard P. Michon_, Oct 31 2012
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