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A174100
Numbers k such that both 2*k + 1 and 6*k + 1 are prime.
2
1, 2, 3, 5, 6, 11, 18, 21, 23, 26, 30, 33, 35, 51, 56, 63, 68, 81, 83, 90, 95, 96, 105, 125, 128, 131, 135, 138, 146, 153, 156, 165, 168, 173, 186, 200, 215, 216, 221, 230, 233, 243, 245, 261, 270, 278, 293, 296, 300, 336, 338, 363, 375, 378, 380, 398
OFFSET
1,2
EXAMPLE
a(1)=1 because 1*2 + 1 = 3 (a prime) and 1*6 + 1 = 7 (also a prime).
MATHEMATICA
Select[Range[400], PrimeQ[2#+1]&&PrimeQ[6#+1]&] (* Harvey P. Dale, Jan 17 2011 *)
CROSSREFS
Sequence in context: A112598 A346721 A078913 * A359599 A114339 A339308
KEYWORD
nonn
AUTHOR
EXTENSIONS
Corrected (118 removed, 132 replaced by 131) by R. J. Mathar, Apr 20 2010
Name edited by Jon E. Schoenfield, May 19 2019
STATUS
approved