A264043 - OEIS

%I #10 Feb 08 2016 20:32:53

%S 6,22,35,46,62,74,82,115,155,166,206,259,262,295,323,355,358,362,395,

%T 466,478,482,502,511,559,562,583,586,611,623,626,671,703,718,731,734,

%U 746,755,763,799,835,838,862,866,886,895,914,923,955,979,982

%N Numbers n such that n and n+3 are consecutive semiprimes.

%H Charles R Greathouse IV, <a href="/A264043/b264043.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) >> n log n. - _Charles R Greathouse IV_, Nov 02 2015

%e 6 and 9 are 2nd and 3rd semiprimes, or 6=A001358(2) and 9=A001358(3);

%e 22=A001358(8) and 25=A001358(9).

%t Flatten[Position[Partition[Table[If[PrimeOmega[n]==2,1,0],{n,1000}], 4,1],_?(#=={1,0,0,1}&)]] (* _Harvey P. Dale_, Feb 08 2016 *)

%o (PARI) for(n=1, 1e3, if(bigomega(n) == 2 && bigomega(n+3) == 2 && bigomega(n+1) !=2 && bigomega(n+2) !=2, print1(n", "))) \\ _Altug Alkan_, Nov 02 2015

%o (PARI) is(n)=if(n%4==2, isprime(n/2) && bigomega(n+3)==2 && bigomega(n+1)!=2, n%4==3 && isprime((n+3)/2) && bigomega(n)==2 && bigomega(n+2)!=2) \\ _Charles R Greathouse IV_, Nov 02 2015

%Y Cf. A001358, A065516, A136196.

%K nonn

%O 1,1

%A _Zak Seidov_, Nov 02 2015