1 files changed, 50 insertions, 0 deletions
diff --git a/euler346.c b/euler346.c
new file mode 100644
index 0000000..dc10d65
--- /dev/null
+++ b/euler346.c
@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+
+#define MAXN 1000000000000
+#define NRUMAX 10000000
+
+long long ru[NRUMAX];
+int nru = 0;
+
+int comp(const void *a, const void *b)
+{
+	long long x = *(long long*)a;
+	long long y = *(long long*)b;
+
+	if (x < y)
+		return -1;
+	else if (x > y)
+		return 1;
+	else 
+		return 0;
+}
+
+int main()
+{
+	long long sum_repunit = 1; /* 1 is a strong repunit */
+	for (int base = 2; base < 1000000; base++) {
+		long long repunit = 1 + base;
+		long long nb = base;
+		while (1) {
+			nb *= base;
+			repunit += nb;
+			if (repunit >= MAXN)
+				break;
+			assert(nru < NRUMAX);
+			ru[nru] = repunit;
+			nru++;
+		}
+	}
+
+	qsort(ru, nru, sizeof(long long), comp);
+
+	printf("Find %d strong repunits.\n", nru + 1);
+	for (int i = 0; i < nru; i++) {
+		if (i > 0 && ru[i] == ru[i-1])
+			continue;
+		sum_repunit += ru[i];
+	}
+	printf("Their sum is %lld\n", sum_repunit);
+}