OFFSET
1,3
COMMENTS
Unrelated: Numbers n such that n + 2^bigomega(n) is either a prime or a semiprime: 1, 2, 3, 5, 6, 7, 9, 10, 11, 13, 15, 17, 18, 19, 21, 22, 23, 25, 27,...
A179384 is a subsequence. - R. J. Mathar, Apr 26 2013
MAPLE
A221865 := proc(n)
option remember;
if n =1 then
0;
else
for a from procname(n-1)+1 do
if not isprime(a) then
if isprime(a+2) or numtheory[bigomega](a+2) = 2 then
return a;
end if;
end if;
end do:
end if;
end proc: # R. J. Mathar, Apr 26 2013
MATHEMATICA
Select[Range[0, 200], !PrimeQ[#]&&PrimeOmega[#+2]<3&] (* Harvey P. Dale, May 05 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Gerasimov Sergey, Apr 18 2013
EXTENSIONS
Corrected by R. J. Mathar, Apr 26 2013
STATUS
approved