

A140077


Numbers n such that n and n+1 have 3 distinct prime factors.


11



230, 285, 429, 434, 455, 494, 560, 594, 609, 615, 644, 645, 650, 665, 740, 741, 759, 804, 805, 819, 825, 854, 860, 884, 902, 935, 945, 969, 986, 987, 1001, 1014, 1022, 1034, 1035, 1044, 1064, 1065, 1070, 1085, 1104, 1105, 1130, 1196, 1209, 1220, 1221
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OFFSET

1,1


COMMENTS

Goldston, Graham, Pintz, & Yildirim prove that this sequence is infinite.  Charles R Greathouse IV, Sep 14 2015


LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..10000
D. A. Goldston, S. W. Graham, J. Pintz, C. Y. Yildirim, Small gaps between almost primes, the parity problem and some conjectures of Erdos on consecutive integers.


MATHEMATICA

a = {}; Do[If[Length[FactorInteger[n]] == 3 && Length[FactorInteger[n + 1]] == 3, AppendTo[a, n]], {n, 1, 100000}]; a (*Artur Jasinski*)
SequencePosition[PrimeNu[Range[1250]], {3, 3}][[All, 1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Feb 27 2017 *)


PROG

(PARI) is(n)=omega(n)==3&&omega(n+1)==3 \\ Charles R Greathouse IV, Sep 14 2015


CROSSREFS

Cf. A074851, A140078, A140079 .
Sequence in context: A177826 A122269 A171666 * A215217 A211711 A211716
Adjacent sequences: A140074 A140075 A140076 * A140078 A140079 A140080


KEYWORD

nonn


AUTHOR

Artur Jasinski, May 07 2008


STATUS

approved



