An algebra problem by Doli Paik

Algebra Level 2

What is the 2018th term of a sequence whose first term is 8161 and every following term is the sum of the cube of the digits of the previous number?

633789 5645 370 5646 633788

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2 solutions

Doli Paik
Jul 7, 2018

8^3+6^3+1^3+1^3=730 7^3+3^3+0^3=370 Similarly the Next term is also 370 as the digits of the Number remains same that is 3,7,0. Thus the answer is 370.

a 1 = 8161 a 2 = 8 3 + 1 3 + 6 3 + 1 3 = 512 + 1 + 216 + 1 = 730 a 3 = 7 3 + 3 3 + 0 3 = 343 + 27 + 0 = 370 a 4 = 3 3 + 7 3 + 0 3 = 27 + 343 + 0 = 370 a 5 = 370 = a 2018 = 370 \begin{aligned} a_1 & = 8161 \\ a_2 & = 8^3+1^3+6^3+1^3 = 512+1+216+1 = 730 \\ a_3 & = 7^3+3^3+0^3 = 343 + 27 + 0 = 370 \\ a_4 & = 3^3+7^3+0^3 = 27+343+0 = 370 \\ a_5 & = 370 \\ \cdots & = \ \cdots \\ a_{2018} & = \boxed{370} \end{aligned}

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