28213981 has 4 divisors (see below), whose sum is σ = 28571200. Its totient is φ = 27856764.

The previous prime is 28213973. The next prime is 28213987. The reversal of 28213981 is 18931282.

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 28213981 - 2³ = 28213973 is a prime.

It is a super-2 number, since 2×28213981² = 1592057447736722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28213987) 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, 178491 + ... + 178648.

It is an arithmetic number, because the mean of its divisors is an integer number (7142800).

Almost surely, 2^28213981 is an apocalyptic number.

It is an amenable number.

28213981 is a deficient number, since it is larger than the sum of its proper divisors (357219).

28213981 is an equidigital number, since it uses as much as digits as its factorization.

28213981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 357218.

The product of its digits is 6912, while the sum is 34.

The square root of 28213981 is about 5311.6834431280. The cubic root of 28213981 is about 304.4304735105.

The spelling of 28213981 in words is "twenty-eight million, two hundred thirteen thousand, nine hundred eighty-one".