A079147 Primes p such that p+1 has at most 2 prime factors, counted with multiplicity; i.e., primes p such that bigomega(p+1) = A001222(p+1) <= 2.

2, 3, 5, 13, 37, 61, 73, 157, 193, 277, 313, 397, 421, 457, 541, 613, 661, 673, 733, 757, 877, 997, 1093, 1153, 1201, 1213, 1237, 1321, 1381, 1453, 1621, 1657, 1753, 1873, 1933, 1993, 2017, 2137, 2341, 2473, 2557, 2593, 2797, 2857, 2917, 3061, 3217, 3253

Offset: 1

Author

Cino Hilliard, Dec 27 2002

Keywords

• easy
• nonn

Comments

Sum of reciprocals ~ 1.266

Examples

			157 is in the sequence because 157 + 1 = 2*79 has 2 prime factors.
		

Crossrefs

Except for 2, this is identical to A005383. Cf. A079148, A079149, A079150.

Programs

Mathematica

Select[Prime[Range[500]],PrimeOmega[#+1]<3&] (* Harvey P. Dale, May 17 2018 *)

PARI

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