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%I #4 Jan 21 2019 19:01:55
%S 2,3,5,7,11,31,71,511,2591,131071,3359231,167247871,8589934591
%N Numbers n such that n == -1 (mod phi(n-1)).
%C This sequence has the terms from A067933 (all primes), plus 511 and 3359231 that are not primes.
%C Checked up to x<70000000
%C a(14) > 10^11. [From _Donovan Johnson_, Aug 08 2010]
%o (PARI) for(x=1,70000000,if(((x)+1)%eulerphi((x)-1)==0,print((x))))
%Y Cf. A067933.
%K nonn
%O 1,1
%A _Jorge Coveiro_, Jul 25 2006
%E a(13) from _Donovan Johnson_, Aug 08 2010
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