Find the odd number / letters / word from the given alternative: 10, 13, 234, 681, 997

Explanation:-

681 is odd number as 10, 12, 234, 681, 997
10 = 1 + 0 = (1)²
13 = 1 + 3 = 4 = (2)²
234 = 2 + 3 + 4 = 9 = (3)2
997 = 9 + 9 + 7 = 25 = (5)²
681 = 6 + 8 + 1 = 15 ≠ (4)²