A280010 Orders of consecutive clusters of non-Chen primes.

1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 1, 1, 3, 1, 1, 2, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 2, 1, 2, 1, 1, 3, 1, 2, 1, 1, 1, 2

Offset: 1

Author

Enrique Navarrete, Feb 21 2017

Keywords

• nonn

Examples

			a(1)=1 since the first cluster consists of the single value p=43.
a(3)=2 since the third cluster consists of the consecutive non-Chen primes {73,79}.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A102540, A280009.

Programs

Mathematica

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

PARI

do(lim)=my(v=List(), u=v, r, s); 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), if(s, listput(v, s); s=0), s++); r=p); u=0; Vec(v) \\ Charles R Greathouse IV, Feb 27 2017