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%I #23 Aug 17 2023 20:43:01
%S 1,0,1,1,1,2,2,2,3,2,2,4,4,4,5,4,4,5,5,6,7,6,6,7,7,6,7,7,7,9,9,9,10,9,
%T 9,10,10,10,11,10,10,12,12,13,14,13,13,14,14,13,14,14,14,15,15,15,16,
%U 15,15,17,17,17,18,17,17,18,18,19,20,19,19,20,20,20,21,21,21,22,22,22,23,22,22,24,24,23
%N Number of remainders occurring only once when dividing n by 1,2,...n.
%C Number of 1's in row n of A072528.
%H Harvey P. Dale, <a href="/A227911/b227911.txt">Table of n, a(n) for n = 1..1000</a>
%e 9 divided by 1,2...9 gives the remainders 0,1,0,1,4,3,2,1,0 of which 2,3,4 occur only once, so a(9)=3.
%t Table[Count[Tally[Mod[n,Range[n]]],_?(#[[2]]==1&)],{n,90}] (* _Harvey P. Dale_, Aug 17 2023 *)
%o (PARI) a(n)=v=vector(n+1);for(d=1,n,t=(n%d)+1;v[t]=v[t]+1);sum(i=1,n,v[i]==1)
%K nonn
%O 1,6
%A _Ralf Stephan_, Oct 13 2013