21428161 has 4 divisors (see below), whose sum is σ = 22119424. Its totient is φ = 20736900.

The previous prime is 21428153. The next prime is 21428189. The reversal of 21428161 is 16182412.

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 21428161 - 2³ = 21428153 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21428131) 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, 345585 + ... + 345646.

It is an arithmetic number, because the mean of its divisors is an integer number (5529856).

Almost surely, 2^21428161 is an apocalyptic number.

It is an amenable number.

21428161 is a deficient number, since it is larger than the sum of its proper divisors (691263).

21428161 is an equidigital number, since it uses as much as digits as its factorization.

21428161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 691262.

The product of its digits is 768, while the sum is 25.

The square root of 21428161 is about 4629.0561672980. The cubic root of 21428161 is about 277.7548388109.

The spelling of 21428161 in words is "twenty-one million, four hundred twenty-eight thousand, one hundred sixty-one".