If by 'perfect number' you mean 'perfect SQUARE', then yes. 49 is an odd number and a perfect square.
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)
It is not yet known:Whether there is an infinite number of even perfect numbersWhether there is any odd perfect number
81 is; Natural number, Perfect-square number, Perfect 4th root number, Perfect totient number, Odd Number, Composite Number, etc.
It is 1! = 1.
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.
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.
A perfect square has an odd number of factors. Factors of numbers always come in pairs -- except for perfect squares. Since the square root of a perfect square is listed only once on the list of factors, it results in a list with an odd number of factors.
a perfect square
A perfect square.