If by 'perfect number' you mean 'perfect SQUARE', then yes. 49 is an odd number and a perfect square.
It is not yet known:Whether there is an infinite number of even perfect numbersWhether there is any odd perfect number
It is unknown whether an odd perfect number actually exists. If an odd perfect number exists it will be extremely large, that is in excess of 10300.
No. Because 7 is not even a perfect number; it is conjectured (not proven) that there are no odd perfect numbers only even ones and 7 is an odd number - it has been proven that if there is an odd perfect number it has to be extremely large, much-much-much larger than 7)
81 is; Natural number, Perfect-square number, Perfect 4th root number, Perfect totient number, Odd Number, Composite Number, etc.
If by 'perfect number' you mean 'perfect SQUARE', then yes. 49 is an odd number and a perfect square.
It is not yet known:Whether there is an infinite number of even perfect numbersWhether there is any odd perfect number
It is unknown whether an odd perfect number actually exists. If an odd perfect number exists it will be extremely large, that is in excess of 10300.
An odd number.
The square of any odd integer is an odd square number. For example, 3^2 = 9.
A perfect square has an odd number of factors.
-1 is an odd number but not a perfect square.
if a number has an odd number of factors it would be a perfect square
if a number has an odd number of factors it would be a perfect square
1 is odd and a perfect square.
Perfect squares are numbers with an odd number of factors.
I would call an odd number factor a factor that is an odd number. I would call a number with an odd number of factors a perfect square.