Nth Star Number

Create a function that takes a positive integer n and returns the nth "star number".

A star number is a centered figurate number that represents a centered hexagram (six-pointed star), such as the one that Chinese checkers is played on.

Examples

starNumber(2) ➞ 13
// n = 2
// 2nd star number = 13

starNumber(3) ➞ 37
// n = 3
// 3rd star number = 37

starNumber(5) ➞ 121
// n = 5
// 5th star number = 121

Notes

• n will always be a positive integer.
• The nth term of a star number can be represented as 6n(n-1) + 1
• See Resources for more information.