OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
MAPLE
filter:= proc(n) local k;
k:= n mod 3;
if k = 0 then isprime(n/3) and isprime((n-1)/2) and numtheory:-bigomega(n-2)=2
elif k= 1 then false
else isprime((n-2)/3) and isprime((n-1)/2) and numtheory:-bigomega(n)=2
fi
end proc:
select(filter, [seq(i, i=3..10000, 4)]); # Robert Israel, Jun 11 2020
MATHEMATICA
upto=5000; p=Prime[Range[PrimePi[upto/2]]]; lim=Floor[Sqrt[upto]]; sp={}; k=0; While[k++; p[[k]]<=lim, sp=Join[sp, p[[k]] *Take[p, {k, PrimePi[upto/p[[k]]]}]]]; sp=Sort[sp]; Transpose[Select [Partition[sp, 3, 1], Last[#]-#[[2]]==#[[2]]-First[#]==1&]][[3]] (* Harvey P. Dale, Mar 21 2011 -- semiprime generating portion of program from A001358 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Mar 08 2006
STATUS
approved