Can you spot the pattern here?

Look at the first few Pythagorean triples: ( 3 , 4 , 5 ) , ( 5 , 12 , 13 ) , ( 7 , 24 , 25 ) , ( 9 , 40 , 41 ) , ( 11 , 60 , 61 ) . (3, 4, 5),\ (5, 12, 13),\ (7, 24, 25),\ (9, 40, 41),\ (11, 60, 61). Can you spot the pattern here?

Let's assume N N is equal to 2 7 ^27 , or 7 7 tetrated to 2 2 . Also, let ( a , b , c ) (a, b, c) deonte the N th N^\text{th} Pythagorean triple.

What is a + b + c ? a + b + c?


The answer is 2712897232656.

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2 solutions

Zico Quintina
May 13, 2018

Another simple way to generate this pattern is to take any odd number as a a , then find a 2 a^2 and split it as evenly as possible into whole numbers b b and c c . For example:

  • a = 13 a = 13 : a 2 = 169 = 84 + 85 \qquad a^2 = 169 = 84 + 85 \qquad \quad generates ( 13 , 84 , 85 ) (13, 84, 85)
  • a = 19 a = 19 : a 2 = 361 = 180 + 181 \qquad a^2 = 361 = 180 + 181 \qquad generates ( 19 , 180 , 181 ) (19, 180, 181)
  • a = 27 a = 27 : a 2 = 729 = 364 + 365 \qquad a^2 = 729 = 364 + 365 \qquad generates ( 27 , 364 , 365 ) (27, 364, 365)

etc. As the last two numbers are consecutive the triples will always be primitive.

The general formula for these triples is ( 2 n + 1 , 2 n 2 + 2 n , 2 n 2 + 2 n + 1 ) (2n + 1, 2n^2 + 2n, 2n^2 + 2n + 1) ; simple algebra proves it generates Pythagorean triples for all n N n \in \mathbb{N} .

For the answer to the question, we need n = 7 7 n=7^7 ; the sum will be 4 n 2 + 6 n + 2 = 4 ( 7 14 ) + 6 ( 7 7 ) + 2 = 2712897232656 4n^2 + 6n + 2 = 4(7^{14}) + 6(7^7) + 2 = \boxed{2712897232656}

Stefan Popescu
May 12, 2018

See my most recent post about Pythagorean Triples for the solution and the rule to the pattern. We have a = 1647087 , b = 1356447792784 , c = 1356447792785 a = 1647087, b = 1356447792784, c = 1356447792785 .

What... HOW IS THIS ONLY LEVEL 2?? Can somenoe pls make it Level 3?

How do you define the 'nth' Pythagorean triple? (8,15,17) or (20,21,29) are Pythagorean Triples,too.

X X - 3 years ago

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The Nth Pythagorean triple ACCORDING TO THE PATTERN. 8, 15, 17 is not part of the pattern. You may want to look at my most recent post if you want to clarify what the pattern does.

Stefan Popescu - 3 years ago

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Thanks,I got it now.

X X - 3 years ago

The sequence of triples you outline appear to be those with shortest side of length 2 N + 1 2N + 1 for positive integers N N , in which case the general formula for the desired sum is ( 2 N + 1 ) ( 2 N + 2 ) (2N + 1)(2N + 2) .

Brian Charlesworth - 3 years ago

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