cp's OEIS Frontend

A259504 Numbers n such that n and n+1 are the product of exactly three (not necessarily distinct) primes.

%I A259504 #30 Jun 27 2019 16:46:13
%S A259504 27,44,75,98,116,124,147,153,164,170,171,174,230,244,245,284,285,332,
%T A259504 356,369,387,425,428,429,434,435,474,506,507,530,548,555,574,595,602,
%U A259504 603,604,605,609,627,637,638,645,651,657,710
%N A259504 Numbers n such that n and n+1 are the product of exactly three (not necessarily distinct) primes.
%C A259504 Conjecture: this sequence is infinite.
%C A259504 Number of terms < 10^k: 0, 4, 63, 727, 7014, 64556, 585725, 5284711, ... . - _Robert G. Wilson v_, Nov 09 2015
%C A259504 a(n) = p^3 where p is prime iff p is in intersection of A065508 and A005383. - _Altug Alkan_, Nov 24 2015
%C A259504 There are 47753279 terms less than 10^9 and 432841730 terms less than 10^10. - _Charles R Greathouse IV_, Jun 27 2019
%H A259504 Charles R Greathouse IV, <a href="/A259504/b259504.txt">Table of n, a(n) for n = 1..10000</a>
%e A259504 27=3*3*3, 28=2*2*7.
%t A259504 Select[Range[1000], 3 == PrimeOmega[#] == PrimeOmega[# + 1] &]
%o A259504 (PARI) forcomposite(n=1, 1e3, if(bigomega(n)==3 && bigomega(n+1)==3, print1(n, ", "))); \\ _Altug Alkan_, Nov 08 2015
%o A259504 (PARI) list(lim)=my(v=List(),was=1,is); forfactored(n=28,lim\1+1, is=vecsum(n[2][,2])==3; if(is && was, listput(v,n[1]-1)); was=is); Vec(v) \\ _Charles R Greathouse IV_, Jun 26 2019
%Y A259504 Intersection of A014612 and A045920.
%Y A259504 Cf. A067813.
%K A259504 nonn
%O A259504 1,1
%A A259504 _Zak Seidov_, Nov 08 2015