^6.^21

It seems like you have entered a mathematical expression or a number, "^6.^21". However, this expression or number is not clear or recognized. In mathematical notation, the caret symbol (^) typically represents an exponent or power. The number after the caret usually denotes the power to which a base is raised. However, in this case, the expression seems to be incomplete or incorrect.

To provide a more accurate answer or explanation, please provide additional context or clarify the expression or number you would like to be explained.