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%I #18 Jun 03 2019 07:56:19
%S 1,3,4,6,11,17,22,23,32,34,40,46,47,48,53,59,60,67,71,83,85,89,94,101,
%T 106,107,115,118,125,128,131,134,136,137,141,142,149,160,166,167,170,
%U 173,177,178,179,184,188,191,192,197,202,204,214,227,230,233,235,236
%N Numbers n such that there is no x < n such that sigma(x) = phi(n).
%H Robert Israel, <a href="/A069825/b069825.txt">Table of n, a(n) for n = 1..1000</a>
%p with(numtheory): A069825 := proc(n) local p,i; p := phi(n); for i from 1 to n-1 do if sigma(i) = p then RETURN(NULL) fi od; n end; # _Peter Luschny_, Nov 02 2010
%p # Alternative:
%p N:= 1000: # to get terms <= N
%p R:= Vector(N):
%p for k from 1 to N-1 do
%p s:= numtheory:-sigma(k);
%p if s <= N and R[s] = 0 then R[s]:= k fi;
%p od:
%p 1, op(select(t -> R[numtheory:-phi(t)]=0, [$2..N])); # _Robert Israel_, Aug 25 2017
%t okQ[n_] := NoneTrue[Range[n-1], DivisorSigma[1,#] == EulerPhi[n]&];
%t Select[Range[250], okQ] (* _Jean-François Alcover_, Jun 03 2019 *)
%o (PARI) for(n=1,600,if(abs(prod(i=1,n-1,eulerphi(n)-sigma(i)))>0,print1(n,",")))
%K easy,nonn
%O 1,2
%A _Benoit Cloitre_, Apr 28 2002