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%I #20 Jan 05 2018 02:56:17
%S 2,3,5,7,13,19,29,37,43,61,67,73,101,109,137,149,157,163,173,193,197,
%T 199,211,229,241,257,277,281,283,313,317,331,337,347,349,353,367,373,
%U 379,397,401,409,421,457,461,463,487,499,509,523,541
%N Primes p such that there is a unique solution to p = sigma(x) - 1.
%H Harry J. Smith, <a href="/A066076/b066076.txt">Table of n, a(n) for n = 1..1000</a>
%F If A066075(m)=1, then p(m) is here.
%t With[{s = KeySort@ PositionIndex@ Array[DivisorSigma[1, #] - 1 &, 10^5]}, Take[#, 51] &@ Keys@ KeySelect[s, PrimeQ@ # && Length@ Lookup[s, #] == 1 &]] (* _Michael De Vlieger_, Jul 16 2017 *)
%o (PARI) { n=0; for (m=1, 10^9, p=prime(m); a=1; for (x=1, p - 1, if (p == (sigma(x) - 1), a++; break)); if (a==1, write("b066076.txt", n++, " ", p); if (n==1000, return)) ) } \\ _Harry J. Smith_, Nov 10 2009
%Y Cf. A000040, A000203, A058340, A066071, A066072, A066073, A066074, A066075, A066076, A066077, A066080.
%K nonn
%O 1,1
%A _Labos Elemer_, Dec 03 2001
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