Question: 
Write a function to find the nth decagonal number.


Model's Code:
def is_num_decagonal(n):
    return n * (4 * n - 3)



Sample Correct Code:
def is_num_decagonal(n): 
	return 4 * n * n - 3 * n 


Asserts:
assert is_num_decagonal(3) == 27
assert is_num_decagonal(7) == 175
assert is_num_decagonal(10) == 370


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

Test 279 of 974: 200/279 (71.68458781362007%): success