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%I #17 Nov 11 2019 10:25:32
%S 5,6,12,14,22,24,26,28,45,48,55,56,67,88,92,94,98,99,101,103,108,114,
%T 116,120,229,236,248,254,265,282,288,298,322,347,362,384,399,420,500,
%U 536,567,615,620,714,835,992,1047,1064,1238,1794,1858,1962,2313,2397
%N Indices k such that A020504(k)=Phi[k](-5) is prime, where Phi is a cyclotomic polynomial.
%H Robert Price, <a href="/A138925/b138925.txt">Table of n, a(n) for n = 1..114</a>
%H Yves Gallot, <a href="http://yves.gallot.pagesperso-orange.fr/papers/cyclotomic.html">Cyclotomic polynomials and prime numbers</a>
%t Select[ Range[ 2000], PrimeQ[ Cyclotomic[#, -5]] &] (* _Robert G. Wilson v_, Mar 25 2012 *)
%o (PARI) for( i=1,999, ispseudoprime( polcyclo(i,-5)) && print1( i",")) /* use ...subst(polcyclo(i),x,-5)... in PARI < 2.4.2 */
%Y Cf. A020504, A138920-A138940.
%K nonn
%O 1,1
%A _M. F. Hasler_, Apr 03 2008
%E a(53)-a(54) from _Robert Price_, Apr 05 2012