This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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. 13
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Sum of reciprocals ~ 1.477. LINKS EXAMPLE 83 is in the sequence because 83 - 1 = 2*41 has 2 prime factors. MATHEMATICA Select[Prime[Range[500]], PrimeOmega[#-1]<3&] (* Harvey P. Dale, May 17 2011 *) PROG (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. CROSSREFS Except for 2 and 3, this is identical to A005385. Cf. A079147, A079149, A079151. Except for 2, this is identical to A005385. Sequence in context: A165802 A107798 A119660 * A107367 A036342 A114421 Adjacent sequences:  A079145 A079146 A079147 * A079149 A079150 A079151 KEYWORD easy,nonn AUTHOR Cino Hilliard, Dec 27 2002 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified October 21 08:47 EDT 2019. Contains 328292 sequences. (Running on oeis4.)