Sierpiński conjecture
In 1960 Wacław Sierpiński (1882-1969) proved the following interesting result:
Theorem:There exist infinitely many odd integers such that is composite for every integer .
A multiplier with this propertyis called a Sierpiński number (http://planetmath.org/SierpinskiNumbers).The Sierpiński problem consists indetermining the smallest Sierpiński number.In 1962, John Selfridge discovered the Sierpiński number ,which is now believed to be in fact the smallest such number.
Conjecture:The integer is the smallest Sierpiński number.
To prove the conjecture, it would be sufficient to exhibita prime for each .