ArithmeticProgression.java

package com.examplehub.maths;

/** https://en.wikipedia.org/wiki/Arithmetic_progression */
public class ArithmeticProgression {

  /**
   * Get nth item.
   *
   * @param firstItem the initial term of an arithmetic progression.
   * @param commonDifference the common difference of successive members.
   * @param nth the nth term of the sequence.
   * @return the nth tern.
   */
  public static int getNth(int firstItem, int commonDifference, int nth) {
    return firstItem + (nth - 1) * commonDifference;
  }

  /**
   * Sum of n items of arithmetic progression.
   *
   * @param firstItem the initial term of an arithmetic progression.
   * @param commonDifference the common difference of successive members.
   * @param n the numbers of arithmetic progression.
   * @return sum of arithmetic progression.
   */
  public static int sum(int firstItem, int commonDifference, int n) {
    return (2 * firstItem + (n - 1) * commonDifference) * n / 2;
  }
}