You can write it like this
IEnumerable<int> range = Enumerable.Range(1, n);
var sum = range.Aggregate(0, (x, y) => x + y);
Sum of squares:
IEnumerable<int> range = Enumerable.Range(1, n);
var sum = range.Aggregate(0, (x, y) => x + y * y);
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…