A079148 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, 7, 11, 23, 47, 59, 83, 107, 167, 179, 227, 263, 347, 359, 383, 467, 479, 503, 563, 587, 719, 839, 863, 887, 983, 1019, 1187, 1283, 1307, 1319, 1367, 1439, 1487, 1523, 1619, 1823, 1907, 2027, 2039, 2063, 2099, 2207, 2447, 2459, 2579, 2819, 2879

Offset: 1

Author

Cino Hilliard, Dec 27 2002

Keywords

• easy
• nonn

Comments

Sum of reciprocals ~ 1.477.

Examples

			83 is in the sequence because 83 - 1 = 2*41 has 2 prime factors.
		

Crossrefs

Except for 2 and 3, this is identical to A005385.

Cf. A079147, A079149, A079151.

Programs

Mathematica

Select[Prime[Range[500]],PrimeOmega[#-1]<3&] (* Harvey P. Dale, May 17 2011 *)

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.