# [Desmos, 53 bytes](https://www.desmos.com/calculator/px4wkubxdo)
```
f(a,b,c,d)=\sum_{x=a}^b\sum_{y=c}^d(x+(x+y)(x+y+1)/2)
```
Order: inclusiveLeftX, inclusiveRightX, inclusiveTopY, inclusiveBottomY