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 A079310 Numbers k such that (6*phi(k)-1, 6*phi(k)+1) is a twin prime pair, where phi is Euler's totient function (A000010). 1
 1, 2, 3, 4, 6, 11, 13, 19, 21, 22, 26, 27, 28, 31, 36, 38, 41, 42, 51, 53, 54, 55, 59, 62, 64, 68, 71, 73, 75, 80, 82, 88, 91, 95, 96, 100, 101, 102, 106, 110, 111, 117, 118, 120, 121, 125, 132, 135, 139, 142, 146, 148, 150, 152, 173, 182, 190, 193, 202, 216, 221, 222 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Ivan Neretin, Table of n, a(n) for n = 1..10000 EXAMPLE phi(19)=18, (6*18-1, 6*18+1) = (107,109) = (A000040(28), A000040(29)), therefore 19 is a term; phi(20)=8, (6*8-1, 6*8+1) = (47,49) = (A000040(15), 7*7), therefore 20 is not a term; phi(21)=12, (6*12-1, 6*12+1) = (71,73) = (A000040(20), A000040(21)), therefore 19 is a term. MATHEMATICA tpQ[n_]:=Module[{c=6EulerPhi[n]}, PrimeQ[c-1]&&PrimeQ[c+1]]; Select[ Range[ 300], tpQ] (* Harvey P. Dale, May 11 2011 *) CROSSREFS Cf. A000010, A001359, A006512, A014574. Sequence in context: A018297 A050886 A341652 * A116853 A342334 A066615 Adjacent sequences:  A079307 A079308 A079309 * A079311 A079312 A079313 KEYWORD nonn AUTHOR Reinhard Zumkeller, Feb 10 2003 STATUS approved

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Last modified April 22 12:32 EDT 2021. Contains 343177 sequences. (Running on oeis4.)