A206347 - OEIS

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A206347

Numbers n such that 10*n+1, 20*n+1, and 30*n+1 are all primes.

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

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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

Amiram Eldar, Table of n, a(n) for n = 1..10000

MATHEMATICA

Select[Range[20000], PrimeQ[10 #+1] && PrimeQ[20 #+1] && PrimeQ[30 #+1]&]

CROSSREFS

Cf. A002997, A046025.

Sequence in context: A365081 A352096 A103246 * A362008 A247316 A072392

Adjacent sequences: A206344 A206345 A206346 * A206348 A206349 A206350

KEYWORD

nonn

AUTHOR

José María Grau Ribas, Feb 06 2012

STATUS

approved