luc040.c

Metadata

• Author — Amit Dutta
• Last updated — 12 Dec 2025
• License — MIT License (See the LICENSE file for details)

Problem Statement

Problem Statement

Ramanujan number (1729) is the smallest number that can be expressed as sum of cubes in two different ways - 1729 can be expressed as 1^3 + 12^3 and 9^3 + 10^3. Write a program to print all such numbers up to a reasonable limit.

Source Code

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#include <stdio.h>

#define limit 100000
#define max_base 47

int main()
{

    long long sum1, sum2;
    int count = 0;

    printf("Ramanujan numbers : \n");

    int found_match;

    for (int a = 1; a <= max_base; a++)
    {
        for (int b = a + 1; b <= max_base; b++)
        {
            sum1 = (long long)a * a * a + (long long)b * b * b;
            if (sum1 > limit)
            {
                break;
            }

            found_match = 0;

            for (int c = a + 1; c <= max_base; c++)
            {
                if (found_match)
                {
                    break;
                }
                for (int d = c + 1; d <= max_base; d++)
                {
                    sum2 = (long long)c * c * c + (long long)d * d * d;
                    if (sum2 > sum1)
                    {
                        break;
                    }
                    if (sum1 == sum2)
                    {
                        count++;
                        printf("(%d.) %lld = %d^3 + %d^3 = %d^3 + %d^3\n", count, sum1, a, b, c, d);

                        found_match = 1;
                        break;
                    }
                }
            }
        }
    }

    printf("-------------------------------\n");
    printf("Search complete.");

    return 0;
}