This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A138939 #15 Nov 11 2019 10:27:04 %S A138939 6,12,18,20,30,36,54,66,118,138,152,182,232,264,336,340,380,414,446, %T A138939 492,540,624,720,762,1066,1094,1098,1170,1230,1254,1320,1428,1546, %U A138939 2018,2574,2724,2804,2920,3074,3316,3646,4124,4132,4186,4620,4802 %N A138939 Indices k such that A019327(k)=Phi[k](9) is prime, where Phi is a cyclotomic polynomial. %H A138939 Robert Price, <a href="/A138939/b138939.txt">Table of n, a(n) for n = 1..64</a> %H A138939 Yves Gallot, <a href="http://yves.gallot.pagesperso-orange.fr/papers/cyclotomic.html">Cyclotomic polynomials and prime numbers</a> %H A138939 <a href="/index/Cy#CyclotomicPolynomialsValuesAtX">Index entries for cyclotomic polynomials, values at X</a> %t A138939 Select[Range[1000], PrimeQ[Cyclotomic[#, 9]] &] %o A138939 (PARI) for( i=1,999, ispseudoprime( polcyclo(i,9)) && print1( i",")) /* use ...subst( polcyclo(i),x,9)... in PARI < 2.4.2 */ %Y A138939 Cf. A019327, A138920-A138940. %K A138939 nonn %O A138939 1,1 %A A138939 _M. F. Hasler_, Apr 03 2008 %E A138939 a(25)-a(46) from _Robert Price_, Apr 28 2012