A264779 - OEIS

A264779

Numbers n for which the numbers 6n+1, 3n+2, 6n+7 are all odd composite squarefree, but not all semiprimes.

183, 249, 361, 371, 413, 459, 487, 501, 515, 525, 609, 613, 639, 697, 749, 763, 795, 823, 893, 911, 931, 1009, 1043, 1051, 1081, 1093, 1213, 1237, 1263, 1271, 1275, 1301, 1373, 1383, 1393, 1399, 1425, 1509, 1513, 1523, 1543, 1561, 1581, 1589, 1617, 1659, 1663

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OFFSET

1,1

LINKS

Peter J. C. Moses, Table of n, a(n) for n = 1..2000

MATHEMATICA

semiPrimeQ:=Last[Total[FactorInteger[#]]]==2&;

A264779=Select[Range[1000], Map[Apply[And, #]&, Transpose[Map[{CompositeQ[#], OddQ[#], SquareFreeQ[#], semiPrimeQ[#]}&, {6#+1, 3#+2, 6#+7}]]]=={True, True, True, False}&]

PROG

(PARI) is(n)={bittest(n, 0)&&Set(apply(issquarefree, n=[3*n+2, 6*n+1, 6*n+7]))==[1]&&vecmax(n=apply(omega, n))>2&&vecmin(n)>1} \\ M. F. Hasler, Nov 25 2015

CROSSREFS

Cf. A001358, A263510, A264778.

Sequence in context: A228535 A248628 A217608 * A133609 A305349 A030465

Adjacent sequences: A264776 A264777 A264778 * A264780 A264781 A264782

KEYWORD

nonn

AUTHOR

Vladimir Shevelev and Peter J. C. Moses, Nov 24 2015

STATUS

approved