In mathematics, a semiprime (also called biprime or 2-almost prime, or pq number) is a natural number that is the product of two (not necessarily distinct) prime numbers. A Finnish engineer, called V.J. Pohjola, on December 16, 2011, published a conjecture for which 216 is the smallest number n, for which n−3, n−2, n−1, n+1, n+2, n+3 are all semiprimes.