28207721 has 2 divisors, whose sum is σ = 28207722. Its totient is φ = 28207720.

The previous prime is 28207717. The next prime is 28207733. The reversal of 28207721 is 12770282.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 25110121 + 3097600 = 5011^2 + 1760^2 .

It is a cyclic number.

It is not a de Polignac number, because 28207721 - 2² = 28207717 is a prime.

It is not a weakly prime, because it can be changed into another prime (28207771) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14103860 + 14103861.

It is an arithmetic number, because the mean of its divisors is an integer number (14103861).

Almost surely, 2^28207721 is an apocalyptic number.

It is an amenable number.

28207721 is a deficient number, since it is larger than the sum of its proper divisors (1).

28207721 is an equidigital number, since it uses as much as digits as its factorization.

28207721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3136, while the sum is 29.

The square root of 28207721 is about 5311.0941433946. The cubic root of 28207721 is about 304.4079565921.

The spelling of 28207721 in words is "twenty-eight million, two hundred seven thousand, seven hundred twenty-one".