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 A206347 n such that 10*n+1, 20*n+1, and 30*n+1 are all primes. 1
 21, 27, 33, 60, 117, 153, 222, 228, 306, 426, 480, 495, 558, 585, 615, 636, 669, 684, 762, 768, 819, 852, 894, 909, 1083, 1125, 1131, 1224, 1239, 1341, 1455, 1512, 1539, 1776, 1812, 1845, 2301, 2484, 2517, 2541, 2604, 2706, 2769, 3093, 3177 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS (10*n+1)*(20*n+1)*(30*n+1) is a Carmichael number for all n in this sequence. Why is (6m+1)*(12m+1)*(18m +1) used to generate Carmichael numbers and never the formula (10m+1)*(20m+1)*(30m+1)? LINKS MATHEMATICA Select[Range[20000], PrimeQ[10 #+1] && PrimeQ[20 #+1] && PrimeQ[30 #+1]&] PROG Cf. A002997, A046025. CROSSREFS Sequence in context: A173836 A064507 A103246 * A072392 A144415 A098898 Adjacent sequences:  A206344 A206345 A206346 * A206348 A206349 A206350 KEYWORD nonn AUTHOR José María Grau Ribas, Feb 06 2012 STATUS approved

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