28021681 has 4 divisors (see below), whose sum is σ = 28673392. Its totient is φ = 27369972.

The previous prime is 28021673. The next prime is 28021703. The reversal of 28021681 is 18612082.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 28021681 - 2³ = 28021673 is a prime.

It is a super-2 number, since 2×28021681² = 1570429212131522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (28021621) 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, 325791 + ... + 325876.

It is an arithmetic number, because the mean of its divisors is an integer number (7168348).

Almost surely, 2^28021681 is an apocalyptic number.

It is an amenable number.

28021681 is a deficient number, since it is larger than the sum of its proper divisors (651711).

28021681 is an equidigital number, since it uses as much as digits as its factorization.

28021681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 651710.

The product of its (nonzero) digits is 1536, while the sum is 28.

The square root of 28021681 is about 5293.5508876368. The cubic root of 28021681 is about 303.7372534971.

The spelling of 28021681 in words is "twenty-eight million, twenty-one thousand, six hundred eighty-one".