Tetranacci Number in Java

In this section, we will learn what is a Tetranacci number and also create Java programs to check if the given number is a Tetranacci number or not. The Tetranacci number program is frequently asked in Java coding interviews and academics.

Tetranacci Number

Tetranacci numbers are similar to the Fibonacci numbers. The only difference is that the Fibonacci number is dependent on the last two Fibonacci numbers, whereas a Tetranacci number is dependent on the last four Tetranacci numbers.

Mathematically, the Tetranacci numbers are represented as:

T(0) = 0,

T(1) = 1,

T(2) = 1,

T(3) = 2,

T(n) = T(n - 4) + T(n - 3) + T(n - 2) + T(n - 1), where n >= 4

Thus,

T(4) = T(0) + T(1) + T(2) + T(3) = 0 + 1 + 1 + 2 = 4

T(5) = T(1) + T(2) + T(3) + T(4) = 1 + 1 + 2 + 4 = 8

T(6) = T(2) + T(3) + T(4) + T(5) = 1 + 2 + 4 + 8 = 15

T(7) = T(3) + T(4) + T(5) + T(6) = 2 + 4 + 8 + 15 = 29

T(8) = T(4) + T(5) + T(6) + T(7) = 2 + 4 + 8 + 15 + 29 = 56

Java Program for Tetranacci Numbers: Iterative Approach

The following program generates the Tetranacci numbers using the mathematical formula defined above.

FileName: TetranacciNumberIterative.java

// A Java program to find the first 20 Tetranacci number
public class TetranacciNumberIterative 
{
// method for finding the Tetranacci number for the number n
int findTetranacciIterative(int n)
{
// the arr is of size 4 
// because the current element is 
// dependent on the last 4 elements
int arr[] = new int[4];
// initializing the array
// with the first four elements 
// defined in the mathematical formula
arr[0] = 0;
arr[1] = 1;
arr[2] = 1;
arr[3] = 2;
if(n <= 3)
{
return arr[n];
}
// loop for finding the next Tetranacci number
for(int i = 4; i <= n; i++)
{
// the current Tetranacci number is dependent on the last 4 elements
int temp = arr[0] + arr[1] + arr[2] + arr[3];
arr[0] = arr[1];
arr[1] = arr[2];
arr[2] = arr[3];
arr[3] = temp;
}
// arr[3] always contain the current Tetranacci number
return arr[3];
}
// main method
public static void main(String argvs[])
{
// creating an object of the class TetranacciNumberIterative
TetranacciNumberIterative obj = new TetranacciNumberIterative();
System.out.println("The first 20 Tetranacci numbers are: ");
// loop for finding the Tetranacci numbers
for(int i = 0; i <= 19; i++)
{
int no = obj.findTetranacciIterative(i);
System.out.print(no + " ");
}
}
}

Output:

The first 20 Tetranacci numbers are: 
0 1 1 2 4 8 15 29 56 108 208 401 773 1490 2872 5536 10671 20569 39648 76424

Java Program for Tetranacci Numbers: Recursive Approach

If we treat the value of the first four Tetranacci numbers as the base case, then the above mentioned mathematically formula turns out to be the recursive formula too to find the other Tetranacci numbers. The following code uses the above mathematical formula to generate the next Tetranacci number recursively.

FileName: TetranacciNumberRecursive.java

// A Java program to find the first 20 Tetranacci number recursively
public class TetranacciNumberRecursive 
{
// method for finding the Tetranacci number for the number n
int findTetranacciRecursive(int n)
{
// these three if conditions are 
// for the first four Tetranacci numbers
// which is also the base case
if(n <= 1)
{
return n;
}
if(n == 2)
{
return 1;
}
if(n == 3)
{
return 2;
}
// the current Tetranacci number is dependent on
// the last four Tetranacci numbers
// finding the next Tetranacci number recursively
return findTetranacciRecursive(n - 1) + 
       findTetranacciRecursive(n - 2) + 
       findTetranacciRecursive(n - 3) +
       findTetranacciRecursive(n - 4);
}
// main method
public static void main(String argvs[])
{
// creating an object of the class TetranacciNumberRecursive
TetranacciNumberRecursive obj = new TetranacciNumberRecursive();
System.out.println("The first 20 Tetranacci numbers are: ");
// loop for finding the Tetranacci numbers
for(int i = 0; i <= 19; i++)
{
int no = obj.findTetranacciRecursive(i);
System.out.print(no + " ");
}
}
}

Output:

The first 20 Tetranacci numbers are: 
0 1 1 2 4 8 15 29 56 108 208 401 773 1490 2872 5536 10671 20569 39648 76424

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Tetranacci Number in Java