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A Composite number which is the Product of two Primes (possibly equal). They correspond to the 2-Almost Primes. The first few are 4, 6, 9, 10, 14, 15, 21, 22, ... (Sloane's A001358).

See also Almost Prime, Chen's Theorem, Composite Number, Prime Number


Sloane, N. J. A. Sequence A001358/M3274 in ``An On-Line Version of the Encyclopedia of Integer Sequences.'' and Sloane, N. J. A. and Plouffe, S. The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.

© 1996-9 Eric W. Weisstein