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%I #15 Apr 15 2018 05:07:49
%S 3,6,7,12,22,27,28,35,41,59,63,69,112,127,132,133,136,140,164,166,202,
%T 215,218,276,288,307,323,334,343,377,383,433,474,479,516,519,521,532,
%U 538,549,575,586,622,647,675,680,692,733,790,815,822,902,909,911,915,952,966,1025,1034,1048,1093
%N Numbers n such that Phi_21(n) is prime, where Phi is the cyclotomic polynomial.
%H G. C. Greubel, <a href="/A250177/b250177.txt">Table of n, a(n) for n = 1..10000</a>
%t a250177[n_] := Select[Range[n], PrimeQ@Cyclotomic[21, #] &]; a250177[1100] (* _Michael De Vlieger_, Dec 25 2014 *)
%o (PARI) {is(n)=isprime(polcyclo(21,n))};
%o for(n=1,100, if(is(n)==1, print1(n, ", "), 0)) \\ _G. C. Greubel_, Apr 14 2018
%Y Cf. A008864 (1), A006093 (2), A002384 (3), A005574 (4), A049409 (5), A055494 (6), A100330 (7), A000068 (8), A153439 (9), A250392 (10), A162862 (11), A246397 (12), A217070 (13), A250174 (14), A250175 (15), A006314 (16), A217071 (17), A164989 (18), A217072 (19), A250176 (20), this sequence (21), A250178 (22), A217073 (23), A250179 (24), A250180 (25), A250181 (26), A153440 (27), A250182 (28), A217074 (29), A250183 (30), A217075 (31), A006313 (32), A250184 (33), A250185 (34), A250186 (35), A097475 (36), A217076 (37), A250187 (38), A250188 (39), A250189 (40), A217077 (41), A250190 (42), A217078 (43), A250191 (44), A250192 (45), A250193 (46), A217079 (47), A250194 (48), A250195 (49), A250196 (50), 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), A251597 (131072), A244150 (524287), A243959 (1048576).
%Y Cf. A085398 (Least k>1 such that Phi_n(k) is prime).
%K nonn
%O 1,1
%A _Eric Chen_, Dec 24 2014
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