Problem 43019. Iterative sum of digits of 2^n number

Created by elias GR

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Given n, calculate the number 2^n (where n>=0) and iterate until the sum of the digits is a single-digit number.
Example:
 Input  n = 7
 Output sum = 2
because 2^7 = 128, and 1+2+8=11 and 1+1=2.

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Last Solution submitted on Dec 09, 2025

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goc3 on 5 Oct 2016

I clarified the problem statement and fixed one test case to make the problem solvable as originally intended.

James on 6 Oct 2016

Anyone else running into an issue with 2^111? I'm getting 2^111 = 2596148429267413814265248164610048, which sums to 143, which sums to 8. The test suite says 9.

Binbin Qi on 11 Nov 2016

The last test is not correct. Could you check it ?

Jean-Marie Sainthillier on 30 May 2017

Yes, this is a sequence (1 2 4 8 7 5 1 2 4 8 7 5 ...)

ChrisR on 12 Jul 2021

The test with n = 111 is still incorrect.

Ramon Villamangca on 27 Oct 2021

is should be 8 for n = 111. am I missing something?

goc3 on 12 Apr 2022

The last test case has been fixed.

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Problem 43019. Iterative sum of digits of 2^n number

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Problem 43019. Iterative sum of digits of 2^n number

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