Question: 
Write a function to find nth centered hexagonal number.


Model's Code:
def centered_hexagonal_number(n):
    return 3 * n * (n - 1) + 1



Sample Correct Code:
def centered_hexagonal_number(n):
  return 3 * n * (n - 1) + 1


Asserts:
assert centered_hexagonal_number(10) == 271
assert centered_hexagonal_number(2) == 7
assert centered_hexagonal_number(9) == 217


Tests:
Test 1 of 3: PASS
Test 2 of 3: PASS
Test 3 of 3: PASS

Test 86 of 974: 65/86 (75.5813953488372%): success