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 A138938 #12 Nov 11 2019 10:26:56 %S A138938 1,3,9,30,42,78,87,138,189,303,318,330,408,462,504,561,1002,1389,1746, %T A138938 1794,2040,2418,2790,3894,4077,4722,6738,10641,14610,14616,15294, %U A138938 16662,18966,19059,26142,27144,28299,31638,33639,39360 %N A138938 Indices k such that A019326(k)=Phi[k](8) is prime, where Phi is a cyclotomic polynomial. %H A138938 Yves Gallot, <a href="http://yves.gallot.pagesperso-orange.fr/papers/cyclotomic.html">Cyclotomic polynomials and prime numbers</a> %H A138938 <a href="/index/Cy#CyclotomicPolynomialsValuesAtX">Index entries for cyclotomic polynomials, values at X</a> %t A138938 Select[Range[1000], PrimeQ[Cyclotomic[#, 8]] &] %o A138938 (PARI) for( i=1,999, ispseudoprime( polcyclo(i,8)) && print1( i",")) /* use ...subst( polcyclo(i),x,8)... in PARI < 2.4.2 */ %Y A138938 Cf. A019326, A138920-A138940. %K A138938 nonn %O A138938 1,2 %A A138938 _M. F. Hasler_, Apr 03 2008 %E A138938 a(17)-a(40) from _Robert Price_, Apr 20 2012