%I #4 Jun 06 2021 11:38:27
%S 31,43,67,71,79,103,131,139,191,223,239,283,311,367,419,431,439,443,
%T 499,599,607,619,643,647,659,683,743,787,823,827,907,947,971,1031,
%U 1039,1087,1091,1103,1163,1223,1259,1399,1427,1447,1499,1511,1543,1559,1571,1579
%N Primes p of the form qrs + 1 where q, r and s are distinct primes.
%C Each composite number qrs = a(n)-1 is a squarefree 3-almost prime. This sequence is a subsequence of A078330 which, besides having 3 as its first term, first differs by including 2311 = 2*3*5*7*11 + 1 (a squarefree 5-almost prime plus 1).
%t With[{nn=50},Take[Union[Select[Times@@@Subsets[Prime[Range[2nn]],{3}]+1,PrimeQ]],nn]] (* _Harvey P. Dale_, Jun 06 2021 *)
%o (PARI) /* Here are five equivalent PARI programs */ forprime(p=2,2400, if(moebius(p-1)==-1 && omega(p-1)==3, print1(p,","))) forprime(p=2,2400, if(moebius(p-1)==-1 && bigomega(p-1)==3, print1(p,","))) forprime(p=2,2400, if(bigomega(p-1)==3 && omega(p-1)==3, print1(p,","))) forprime(p=2,2400, if(omega(p-1)==3 && issquarefree(p-1), print1(p,","))) forprime(p=2,2400, if(bigomega(p-1)==3 && issquarefree(p-1), print1(p,",")))
%Y Cf. A078330 (primes p with mu(p-1) = -1).
%K nonn
%O 1,1
%A _Rick L. Shepherd_, Jun 18 2004