28216821 has 16 divisors (see below), whose sum is σ = 40086144. Its totient is φ = 17593344.

The previous prime is 28216817. The next prime is 28216847. The reversal of 28216821 is 12861282.

It is not a de Polignac number, because 28216821 - 2² = 28216817 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28216421) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6861 + ... + 10173.

It is an arithmetic number, because the mean of its divisors is an integer number (2505384).

Almost surely, 2^28216821 is an apocalyptic number.

It is an amenable number.

28216821 is a deficient number, since it is larger than the sum of its proper divisors (11869323).

28216821 is a wasteful number, since it uses less digits than its factorization.

28216821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3500.

The product of its digits is 3072, while the sum is 30.

The square root of 28216821 is about 5311.9507716092. The cubic root of 28216821 is about 304.4406877554.

The spelling of 28216821 in words is "twenty-eight million, two hundred sixteen thousand, eight hundred twenty-one".