Every ``large'' Even Integer may be written as where is a Prime and is the Set of Semiprimes (i.e., 2-Almost Primes).
See also Almost Prime, Prime Number, Semiprime
References
Rivera, C. ``Problems & Puzzles (Conjectures): Chen's Conjecture.''
http://www.sci.net.mx/~crivera/conjectures/conj_002.htm.