Problem 1084. Square Digits Number Chain Terminal Value (Inspired by Project Euler Problem 92)

Created by @bmtran (Bryant Tran)

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Given a number n, return the terminal value of the number chain formed by summing the square of the digits. According to the Project Euler problem, this number chain always terminates with either 1 or 89.

Project Euler Problem 92: Link

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Last Solution submitted on Dec 12, 2019

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M on 31 Oct 2017

Let consider the case x=954

954 -> 122 -> 9 -> 81 -> 65 -> 61 -> 37 -> 58 -> 89 -> 145 -> 42 -> 20 -> 4 -> 16 -> 37

So 37 is seen twice, it should end up with 37, no ?

Eric Lee on 9 Dec 2017

No, 89 shows up before 37 does

David Verrelli on 13 Mar 2018

By the description at ProjectEuler.net, it seems M is correct in their statement. The description there reads: "continuously [...] form a new number until it [that number just formed] has been seen before." That is exactly what M has done. Project Euler says furthermore: "[...] EVERY starting number will eventually arrive at 1 or 89." That is _not_ the same as stating: "this number chain always terminates with either 1 or 89". The key difference is in "arrives at" (the number appears) versus "terminates with" (the number is the first to appear twice in the sequence). In M's example, the sequence truly 'terminates with' 37 (as M said), but before it terminates the sequence had 'arrived at' 89.

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Aurelien Queffurust on 17 Dec 2012

This solution requires Neural Network Toolbox

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plus15 poor_problem_statement projecteuler

Problem 1084. Square Digits Number Chain Terminal Value (Inspired by Project Euler Problem 92)

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Last 200 Solutions

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Problem Recent Solvers146

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Problem 1084. Square Digits Number Chain Terminal Value (Inspired by Project Euler Problem 92)

Solution Stats

Last 200 Solutions

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Solution Comments

Problem Recent Solvers146

Suggested Problems

More from this Author56

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