28206721 has 9 divisors (see below), whose sum is σ = 29076931. Its totient is φ = 27362272.

The previous prime is 28206707. The next prime is 28206749. The reversal of 28206721 is 12760282.

The square root of 28206721 is 5311.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 497025 + 27709696 = 705^2 + 5264^2 .

It is not a de Polignac number, because 28206721 - 2⁹ = 28206209 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 28206721.

It is not an unprimeable number, because it can be changed into a prime (28206701) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 249561 + ... + 249673.

Almost surely, 2^28206721 is an apocalyptic number.

28206721 is the 5311-st square number.

28206721 is the 2656-th centered octagonal number.

It is an amenable number.

28206721 is a deficient number, since it is larger than the sum of its proper divisors (870210).

28206721 is an frugal number, since it uses more digits than its factorization.

28206721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 320 (or 160 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 28.

The cubic root of 28206721 is about 304.4043593317.

The spelling of 28206721 in words is "twenty-eight million, two hundred six thousand, seven hundred twenty-one".