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 A138937 #13 Nov 11 2019 10:26:45 %S A138937 5,6,13,18,21,28,30,34,36,46,48,50,54,55,58,63,76,84,94,105,122,131, %T A138937 148,149,224,280,288,296,332,352,456,528,531,581,650,654,730,740,759, %U A138937 1026,1047,1065,1460,1660,1699,1959,2067,2260,2380,2665,2890,3238,4020 %N A138937 Indices k such that A019325(k)=Phi[k](7) is prime, where Phi is a cyclotomic polynomial. %H A138937 Robert Price, <a href="/A138937/b138937.txt">Table of n, a(n) for n = 1..95</a> %H A138937 Yves Gallot, <a href="http://yves.gallot.pagesperso-orange.fr/papers/cyclotomic.html">Cyclotomic polynomials and prime numbers</a> %H A138937 <a href="/index/Cy#CyclotomicPolynomialsValuesAtX">Index entries for cyclotomic polynomials, values at X</a> %t A138937 Select[Range[1000], PrimeQ[Cyclotomic[#, 7]] &] %o A138937 (PARI) for( i=1,999, ispseudoprime( polcyclo(i,7)) && print1( i",")) /* use ...subst(polcyclo(i),x,7)... in PARI < 2.4.2 */ %Y A138937 Cf. A019325, A138920-A138940. %K A138937 nonn %O A138937 1,1 %A A138937 _M. F. Hasler_, Apr 03 2008 %E A138937 a(40)-a(53) from _Robert Price_, Apr 18 2012