Question

How to find the first integer equal to the sum of its digits raised to some power in Java

Answer 1

public class DigitPower {

    // compute sum of digits
    static long digitSum(long n) {
        long s = 0;

        while (n > 0) {
            s += n % 10;
            n /= 10;
        }

        return s;
    }

    public static void main(String[] args) {
        for (long n = 2; ; n++) {
            long s = digitSum(n);

            // Try powers k = 2..10 (enough for reasonable ranges)
            long p = s * s;
            for (int k = 2; k <= 10; ++k) {
                if (p == n) {
                    System.out.println("Found: " + n +
                                       " = (" + s + ")^" + k);
                    return;
                }
                p *= s; // next power
            }
        }
    }
}



/*
run:

Found: 81 = (9)^2

*/

 

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