|
%I #11 Nov 15 2021 16:25:08
%S 2,3,5,7,11,23,47,59,83,107,167,179,227,263,347,359,383,467,479,503,
%T 563,587,719,839,863,887,983,1019,1187,1283,1307,1319,1367,1439,1487,
%U 1523,1619,1823,1907,2027,2039,2063,2099,2207,2447,2459,2579,2819,2879
%N 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.
%C Sum of reciprocals ~ 1.477.
%e 83 is in the sequence because 83 - 1 = 2*41 has 2 prime factors.
%t Select[Prime[Range[500]],PrimeOmega[#-1]<3&] (* _Harvey P. Dale_, May 17 2011 *)
%o (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.
%Y Except for 2 and 3, this is identical to A005385.
%Y Cf. A079147, A079149, A079151.
%K easy,nonn
%O 1,1
%A _Cino Hilliard_, Dec 27 2002
|
