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 A250176 #24 May 21 2018 03:24:35 %S A250176 4,9,11,16,19,26,34,45,54,70,86,91,96,101,105,109,110,119,120,126,129, %T A250176 139,141,149,171,181,190,195,215,229,260,276,299,305,309,311,314,319, %U A250176 334,339,369,375,414,420,425,444,470,479,485,506,519,534,540,550 %N A250176 Numbers n such that Phi_20(n) is prime, where Phi is the cyclotomic polynomial. %H A250176 G. C. Greubel, <a href="/A250176/b250176.txt">Table of n, a(n) for n = 1..10000</a> %t A250176 Select[Range[600], PrimeQ[Cyclotomic[20, #]] &] (* _Vincenzo Librandi_, Jan 16 2015 *) %o A250176 (PARI) isok(n) = isprime(polcyclo(20, n)); \\ _Michel Marcus_, Sep 29 2015 %Y A250176 Cf. A008864 (1), A006093 (2), A002384 (3), A005574 (4), A049409 (5), A055494(6), A100330 (7), A000068 (8), A153439 (9), A246392 (10), A162862(11), A246397 (12), A217070 (13), A006314 (16), A217071 (17), A164989(18), A217072 (19), A217073 (23), A153440 (27), A217074 (29), A217075(31), A006313 (32), A097475 (36), A217076 (37), A217077 (41), A217078(43), A217079 (47), A217080 (53), A217081 (59), A217082 (61), A006315(64), A217083 (67), A217084 (71), A217085 (73), A217086 (79), A153441(81), A217087 (83), A217088 (89), A217089 (97), A006316 (128), A153442(243), A056994 (256), A056995 (512), A057465 (1024), A057002 (2048), A088361 (4096), A088362 (8192), A226528 (16384), A226529 (32768), A226530(65536). %K A250176 nonn %O A250176 1,1 %A A250176 _Eric Chen_, Dec 24 2014 %E A250176 More terms from _Vincenzo Librandi_, Jan 16 2015