Sum of all the multiples of 3 and 7 below N | Java program to find the sum of all multiples of 3 and 7 below N ; Function to find sum of AP series ; Number of terms ; Function to find the sum of all multiples of 3 and 7 below N ; Since , we need the sum of multiples less than N ; Driver code
import java . util . * ; class solution { static long sumAP ( long n , long d ) { n /= d ; return ( n ) * ( 1 + n ) * d / 2 ; } static long sumMultiples ( long n ) { n -- ; return sumAP ( n , 3 ) + sumAP ( n , 7 ) - sumAP ( n , 21 ) ; } public static void main ( String args [ ] ) { long n = 24 ; System . out . println ( sumMultiples ( n ) ) ; } }