login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A264779 Numbers n for which the numbers 6n+1, 3n+2, 6n+7 are all odd composite squarefree, but not all semiprimes. 4
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 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 16 06:46 EDT 2019. Contains 324145 sequences. (Running on oeis4.)