As my backgroud is backend engineer, I only gave the answer of the question No. 1,4,5.
question 1: Three ways to sum n
use formula, loop, recursion to give the answer
Here is the test result when n = 100
question 4: Interacting with Chain
using the abi and bin file of the contract to generate the go file : Token.go
then use golang to interact with contract
the result is