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%I #9 Jul 28 2019 16:38:40
%S 3,7,13,19,41,0,37,31,113,43,101,71,73,67,61,79,97,131,109,103,0,0,0,
%T 191,0,139,677,127,0,419,157,0,193,0,0,151,0,0,0,199,401,683,181,0,
%U 281,0,0,431,0,283,277,0,0,659,461,0,241,211,0,743,313,0,349,271,641,827
%N Least prime p for which (p-1)/2 - phi(p-1) = n, or 0 if there is no such prime.
%C The graph of this sequence shows that for n>8 either a(n)=0 or a(n)<=1+n^2. See A098006 for the values of (p-1)/2 - phi(p-1) for odd primes p. Sequence A098047 lists the n for which a(n)=0. A134854(n)=a(2^(n-1)).
%H T. D. Noe, <a href="/A134765/b134765.txt">Table of n, a(n) for n = 0..10000</a>
%H T. D. Noe, <a href="http://www.sspectra.com/math/A098006.pdf">Finding primes p for which (p-1)/2 - phi(p-1) = k</a>
%H T. D. Noe, <a href="http://www.sspectra.com/math/A134765.gif">Graph for n <= 50000</a>
%t nn=1000; lc=Table[0,{nn}]; Do[p=Prime[n]; r=(p-1)/2-EulerPhi[p-1]; If[0<r<=nn && lc[[r]]==0, lc[[r]]=p], {n,2,PrimePi[1+nn^2]}]; PrependTo[lc,3]
%K nonn
%O 0,1
%A _T. D. Noe_, Nov 13 2007, Nov 19 2007