A rational number is defined as a number that can be expressed as the quotient of two integers (i.e., a fraction), where the denominator is not zero.
The number you provided, 6.239654a, contains the letter "a," which suggests that it may be a variable rather than a specific numerical value. If "a" is a symbol representing a non-integer value, then 6.239654a may not be a rational number.
However, if "a" is a specific rational number, then 6.239654a could also be rational, as the multiplication of a rational number with another rational number (in this case, 6.239654 and whatever value "a" represents) will result in a rational number.
To determine if 6.239654a is rational, we must first clarify what "a" represents. If "a" is specified or if it takes values that keep the expression rational, then we can conclude if 6.239654a is rational or not.