Possible Duplicate:
What is the term for a factorial type operation, but with summation instead of products?
I am looking for the name of an operation similar to factorial.
Factorial would be like: 6! = 6*5*4*3*2*1
but if the operator is "+" and not "*", like: 6+5+4+3+2+1
What would I call this?
Edit: Sorry, it seems this was a duplicate question. The answer appears to be "nth triangular number". Although that's really not as satisfying and concise as the word "factorial".