Try reducing computation by finding a closed form instead of writing a loop. Here, the closed form is f(n) = n*(n+1) (e.g. f(100) = 100*101 = 10100):

f(n) = n*(n+1)

f(100) = 100*101 = 10100

f(n) = S[1..n] 2*i definition = 2 * S[1..n] i pull out the coefficient = 2 * n*(n+1)/2 by triangular number formula = n*(n+1) cancel the twos

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## re: That programming book you never finished VIEW POST

VIEW FULL DISCUSSIONTry reducing computation by finding a closed form instead of writing a loop. Here, the closed form is

`f(n) = n*(n+1)`

(e.g.`f(100) = 100*101 = 10100`

):