A079150 - OEIS

A079150

Primes p such that p+1 has at most 3 prime factors, counted with multiplicity; i.e., primes p such that bigomega(p+1) = A001222(p+1) <= 3.

%I #13 Jan 13 2020 14:17:11

%S 2,3,5,7,11,13,17,19,29,37,41,43,61,67,73,97,101,109,113,137,157,163,

%T 173,181,193,211,229,241,257,277,281,283,313,317,331,337,353,373,397,

%U 401,409,421,433,457,523,541,547,577,601,613,617,641,653,661,673,677

%N Primes p such that p+1 has at most 3 prime factors, counted with multiplicity; i.e., primes p such that bigomega(p+1) = A001222(p+1) <= 3.

%H Daniel Starodubtsev, <a href="/A079150/b079150.txt">Table of n, a(n) for n = 1..10000</a>

%e 173 is in the sequence because 173+1 = 2*3*29 has 3 prime factors.

%t Select[Prime[Range[200]],PrimeOmega[#+1]<4&] (* _Harvey P. Dale_, Feb 02 2012 *)

%o (PARI) s(n) = {sr=0; ct=0; forprime(x=2,n, if(bigomega(x+1) < 4, print1(x" "); sr+=1.0/x; ct+=1; ); ); print(); print(ct" "sr); } \\ Lists primes p<=n such that p+1 has at most 3 prime factors.

%Y Cf. A001222, A079147, A079151, A079152, A079153.

%K easy,nonn

%O 1,1

%A _Cino Hilliard_, Dec 27 2002