A famous conjecture.
There are many unproved conjectures regarding prime numbers. One of these was made by Christian Goldbach (1690-1764) in 1742 in a letter to the great Swiss mathematician Euler.
Goldbach had observed that every even integer, except 2,
seemed representable as the sum of two primes. Thus 4 = 2 + 2, 6 = 3 + 3, 8 = 5 + 3,...,
48 = 29 + 19,..., 100 = 97 + 3, and so forth.
Goldbach seems to have been an industrious correspondent and to have had the respect of many of the top mathematicians of his day. It was in a letter to Goldbach in 1746, for example, that Euler first announced his remarkable discovery thatii (where i= I/ - 1) is a real number. But today, about the only mention of Goldbach in the history of mathematics concerns his teasing conjecture given above.