const sumFrom1ToN = n => (n * (n + 1)) / 2;
This will work with any number of input numbers, as long as input starts from 1 to n and they are all integers.
Sample Runs: sumFrom1ToN(10); // 55 sumFrom1ToN(5); // 15
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This will work with any number of input numbers, as long as input starts from 1 to n and they are all integers.
Sample Runs:
sumFrom1ToN(10); // 55
sumFrom1ToN(5); // 15