Birch and Swinnerton-Dyer Conjecture
Establish the Birch and Swinnerton-Dyer Conjecture by proving that for elliptic curves the order of vanishing of the associated L-function L(s) at s = 1 equals the rank of the curve.
References
In the twentieth century, Birch and Swinnerton-Dyer plotted, using the earliest computers of the 1960s, ranks and other quantities for elliptic curves, and conjectured that the order of vanishing of the L-function $L(s)$ for the curve at $s \rightarrow 1$ equals to the rank. This observation is the the now celebrated BSD Conjecture that bears their name; it is a Millennium Prize problem and central to modern mathematics.
One needs to bear in mind that two of the remaining six Millennium Problems - the Riemann Hypothesis and the Birch--Swinnerton-Dyer (BSD) Conjecture - arose from mathematical experimentation by listing the first zeroes or by plotting rank and conductor.
Therefore, in spite of various decades of high-level research, the conjecture is still widely open.