The numberOfBuckets parameter say into how many equally-sized intervals should the range of data be split. Then histogram counts how many numbers from data fall into each bucket.
Try:
var v = DenseVector.Create(10, i => i+1);
Console.WriteLine(new Histogram(v, 5));
Maybe you want a histogram of natural numbers where each bucket contains the number of occurrences of a particular number (With some buckets possibly empty)? Then set numberOfBuckets to max-min+1.