Trinomial Triangle
By M.C. Pinto, UNILA 
Brazil
By M.C. Pinto, UNILA Brazil
The trinomial triangle is a number triangle of trinomial coefficients. It can be obtained by starting with a row containing a single "1" and the next row containing three 1s and then letting subsequent row elements be computed by summing the elements above to the left, directly above, and above to the right:
The first row of the trinomial triangle is numbered as zero, the second row is numbered as one and so on.
Given the row number R, you are asked to write a program that prints the sum of its elements. For instance, the sum of elements at row 2 is 9 = 1 + 2 + 3 + 2 + 1.
The input is the row number R (0 ≤ R ≤ 20).
The output is the sum of all elements at row R. Don't forget the end-of-line character after printing the sum.
| Input Samples | Output Samples |
|
0 |
1 |
|
1 |
3 |
|
2 |
9 |