28990721 has 4 divisors (see below), whose sum is σ = 29774292. Its totient is φ = 28207152.

The previous prime is 28990711. The next prime is 28990727. The reversal of 28990721 is 12709982.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 27415696 + 1575025 = 5236^2 + 1255^2 .

It is a cyclic number.

It is not a de Polignac number, because 28990721 - 2⁶ = 28990657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28990727) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 391730 + ... + 391803.

It is an arithmetic number, because the mean of its divisors is an integer number (7443573).

Almost surely, 2^28990721 is an apocalyptic number.

It is an amenable number.

28990721 is a deficient number, since it is larger than the sum of its proper divisors (783571).

28990721 is an equidigital number, since it uses as much as digits as its factorization.

28990721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 783570.

The product of its (nonzero) digits is 18144, while the sum is 38.

The square root of 28990721 is about 5384.3032046867. The cubic root of 28990721 is about 307.1989112250.

The spelling of 28990721 in words is "twenty-eight million, nine hundred ninety thousand, seven hundred twenty-one".