A280009 - OEIS

%I #22 Mar 05 2017 05:39:03

%S 13,3,2,2,1,8,1,1,3,3,1,2,4,1,3,1,2,2,1,1,3,1,2,1,8,1,6,1,1,2,3,2,1,1,

%T 2,2,5,3,1,3,1,2,4,4,1,1,1,2,1,1,1,2,1,1,3,1,1,2,5,1,3,3,1,1

%N Orders of consecutive clusters of Chen primes.

%H Charles R Greathouse IV, <a href="/A280009/b280009.txt">Table of n, a(n) for n = 1..10000</a>

%t Length /@ DeleteCases[Split@ Table[Boole@ And[# != 1, PrimeOmega@ # <= 2] &[# + 2] &@ Prime@ n, {n, 300}], k_ /; Total@ k == 0] (* _Michael De Vlieger_, Feb 27 2017 *)

%o (PARI) do(lim)=my(v=List(),u=v,r,s=1); forprime(p=2,lim\2, forprime(q=2,min(lim\p,p), listput(u,p*q))); u=Set(u); r=3; forprime(p=5,lim, if(p-r==2 || setsearch(u, r+2), s++, if(s, listput(v, s); s=0)); r=p); u=0; Vec(v) \\ _Charles R Greathouse IV_, Feb 27 2017

%Y Cf. A109611.

%K nonn

%O 1,1

%A _Enrique Navarrete_, Feb 21 2017