I have the following Shell sort code in Java but how can I change to sizes of 3n + 1

import java.util.Arrays; // Shell sort class ShellSort { // Rearrange elements at each n/2, n/4, n/8, ... intervals void shellSort(int array[], int n) { for (int interval = n / 2; interval > 0; interval /= 2) { for (int i = interval; i < n; i += 1) { int temp = array[i]; int j; for (j = i; j >= interval && array[j - interval] > temp; j -= interval) { array[j] = array[j - interval]; } array[j] = temp; } } } // Driver code public static void main(String args[]) { int[] data = { 9, 8, 3, 7, 5, 6, 4, 1 }; int size = data.length; ShellSort ss = new ShellSort(); ss.shellSort(data, size); System.out.println("Sorted Array in Ascending Order: "); System.out.println(Arrays.toString(data)); } }