What you’re looking for is the Aggregate function
int modValue = ints.Aggregate(1, (x,y) => x * y);
The Aggregate function takes in an initial accumulator value and then applies an operation to every value in the enumeration creating a new accumulator value. Here we start with 1 and then multiply ever value by the current value of the accumulator.
Note: In the case of an empty ints value this will return 1. This may or may not be correct for your situation.