28212391 has 4 divisors (see below), whose sum is σ = 28289632. Its totient is φ = 28135152.

The previous prime is 28212341. The next prime is 28212403. The reversal of 28212391 is 19321282.

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

It is a cyclic number.

It is not a de Polignac number, because 28212391 - 2⁹ = 28211879 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28212311) 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, 38070 + ... + 38803.

It is an arithmetic number, because the mean of its divisors is an integer number (7072408).

Almost surely, 2^28212391 is an apocalyptic number.

28212391 is a deficient number, since it is larger than the sum of its proper divisors (77241).

28212391 is an equidigital number, since it uses as much as digits as its factorization.

28212391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77240.

The product of its digits is 1728, while the sum is 28.

The square root of 28212391 is about 5311.5337709554. The cubic root of 28212391 is about 304.4247546727.

The spelling of 28212391 in words is "twenty-eight million, two hundred twelve thousand, three hundred ninety-one".