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A079310 Numbers n such that (6*phi(n)-1,6*phi(n)+1) is a twin prime pair, where phi is Eulers' 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. A001359, A006512, A014574.

Sequence in context: A245569 A018297 A050886 * A116853 A066615 A133951

Adjacent sequences:  A079307 A079308 A079309 * A079311 A079312 A079313

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Feb 10 2003

STATUS

approved

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Last modified February 16 04:34 EST 2019. Contains 320140 sequences. (Running on oeis4.)