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| -rwxr-xr-x | challenge-147/steven-wilson/javascript/ch-02.js | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/challenge-147/steven-wilson/javascript/ch-02.js b/challenge-147/steven-wilson/javascript/ch-02.js new file mode 100755 index 0000000000..36fadd5903 --- /dev/null +++ b/challenge-147/steven-wilson/javascript/ch-02.js @@ -0,0 +1,38 @@ +#!/usr/bin/env node +// Week 147 Task 2 +// Pentagon Numbers +// Write a sript to find the first pair of Pentagon Numbers +// whose sum and difference are also a Pentagon Number. +// Answer: First pair is 1560090 and 7042750 + +var pentagonal_numbers = [1] +var pair_found = false +var number = 2 + +while (!pair_found) { + let next_pn = pentagonal_number(number) + for (let i = 0; i < pentagonal_numbers.length; i++) { + if ((is_pentagonal_number(next_pn - pentagonal_numbers[i])) && + (is_pentagonal_number(next_pn + pentagonal_numbers[i]))) { + console.log('First pair are ' + pentagonal_numbers[i] + ' and ' + next_pn) + pair_found = true + break + } + } + pentagonal_numbers.push(next_pn) + number++ +} + +function pentagonal_number (number) { + return ( ( 3 * ( number * number ) ) - number ) / 2 +} + +function is_pentagonal_number (number) { + let remainder = ( Math.sqrt( 24 * number + 1 ) + 1 ) % 6; + if ( remainder > 0 ) { + return false + } + else { + return true + } +} |