%I #24 May 21 2018 03:24:35
%S 4,9,11,16,19,26,34,45,54,70,86,91,96,101,105,109,110,119,120,126,129,
%T 139,141,149,171,181,190,195,215,229,260,276,299,305,309,311,314,319,
%U 334,339,369,375,414,420,425,444,470,479,485,506,519,534,540,550
%N Numbers n such that Phi_20(n) is prime, where Phi is the cyclotomic polynomial.
%H G. C. Greubel, <a href="/A250176/b250176.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Range[600], PrimeQ[Cyclotomic[20, #]] &] (* _Vincenzo Librandi_, Jan 16 2015 *)
%o (PARI) isok(n) = isprime(polcyclo(20, n)); \\ _Michel Marcus_, Sep 29 2015
%Y 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 nonn
%O 1,1
%A _Eric Chen_, Dec 24 2014
%E More terms from _Vincenzo Librandi_, Jan 16 2015