OFFSET
1,2
COMMENTS
omega is the function in A001221. If there are infinitely many primes p such that p and 2p-1 are primes (see A005382), then this sequence is infinite. Proof: the numbers of the form 4p are in a subsequence if p and 2p-1 are both prime, because from the property that omega(4p) = 2 and omega(p(2p-1)) = 2, if n = 4p then omega(n-omega(n)) = omega(4p - 2) = omega(2(2p-1)) = 2 = omega(n).
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..5000
EXAMPLE
12 is in the sequence because omega(12) = 2, omega(12 - 2) = omega(10) = 2.
MATHEMATICA
Select[Range[10^4], PrimeNu[#]==PrimeNu[#-PrimeNu[#]]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Feb 14 2012
STATUS
approved