Formula for Counting the sum of a number range

[user180]

Hello,

Can someone please share the formula for ‘Counting the sum of a number range’ ?
For eg. What is the sum of numbers from 1 to 150?

Many thanks!

[user461]

If it is starting from 1, you can use the formula n(n+1)/2, where n is 150 in the above example case

[user180]

Thanks a lot!