If we have a name and notation for the product of natural numbers up to and including n (factorial and !), then what is the name and shorthand for the sum of natural numbers up to and including n?
(I know about triangular numbers, but that's not a name for the expression that sums the corresponding series.)
Answer
Thanks for the hint, Peter Woolfitt. Found that reference material, "The ARML Power Contest" By Thomas Kilkelly. Chapter 32 discusses the origins of the name deltorial and provides the notation $\Delta_n$ . The use of the name and notation are not mainstream, that's for sure. Does that make it any less valid?
Available on Google Books: full text
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