New year raised to itself

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Let N = 201 4 2014 2014^{2014}

Let A be the sum of digits of N. Let B be the sum of digits of A. Let C be the sum of digits of B.

Find C.


The answer is 7.

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1 solution

Pi Han Goh
Dec 25, 2013

Because 2014 m o d 9 = 7 2014 \bmod {9} = 7 , the sum of digits of 201 4 2014 2014^{2014} divided by 9 9 gives a remainder of 7 7 . So, A B C 7 ( m o d 9 ) A \equiv B \equiv C \equiv 7 \pmod {9}

The number of digits of 201 4 2014 2014^{2014} is log 10 201 4 2014 = 2014 log 10 2014 = 6655 \lceil \log_{10} 2014^{2014} \rceil = \lceil 2014 \log_{10} 2014 \rceil = 6655

max ( A ) = 9 × 6655 = 59895 \text{max} (A) = 9 \times 6655 = 59895

max ( B ) \text{max} (B) occurs when A = 49999 A = 49999 , max ( B ) = 4 + 9 + 9 + 9 + 9 = 40 \text{max} (B) = 4 + 9 + 9 + 9 + 9 = 40

max ( C ) \text{max} (C) occurs when B = 39 B = 39 , max ( C ) = 3 + 9 = 12 \text{max} (C) = 3+9 = 12

Because 1 C 12 1 \leq C \leq 12 and C ( m o d 9 ) = 7 C \pmod {9} = 7 , so C = 7 C = \boxed{7} only.

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