%I A138920
%S A138920 4,5,7,12,19,24,31,36,38,46,48,53,67,75,78,120,186,196,293,320,327,369,
%T A138920 634,641,713,770,931
%N A138920 Indices k such that A020509(k)=Phi[k](-10) is prime, where Phi is a cyclotomic 
               polynomial.
%C A138920 "Unique [period] primes" (A040017) are often of the form Phi[k](10) or 
               Phi[k](-10).
%H A138920 C. Caldwell, <a href="http://primes.utm.edu/glossary/page.php?sort=UniquePrime">
               Unique Primes</a>.
%H A138920 <a href="Sindx_Cy.html#CyclotomicPolynomialsValuesAtX">Index entries 
               for cyclotomic polynomials, values at X</a>
%o A138920 (PARI) for( i=1,999, is/*pseudo*/prime( polcyclo(i,-10)) && print1( i",
               ")) /* for PARI < 2.4.2 use ...subst(polcyclo(i,x),x,-10)... */
%Y A138920 Cf. A019328, A040017, A138940.
%Y A138920 Sequence in context: A160934 A032390 A112918 this_sequence A048224 A064237 
               A139373
%Y A138920 Adjacent sequences: A138917 A138918 A138919 this_sequence A138921 A138922 
               A138923
%K A138920 nonn,more
%O A138920 1,1
%A A138920 M. F. Hasler (www.univ-ag.fr/~mhasler), Apr 03 2008