21428749 has 4 divisors (see below), whose sum is σ = 21927136. Its totient is φ = 20930364.

The previous prime is 21428747. The next prime is 21428791. The reversal of 21428749 is 94782412.

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 21428749 - 2¹ = 21428747 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 (21428747) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 249129 + ... + 249214.

It is an arithmetic number, because the mean of its divisors is an integer number (5481784).

Almost surely, 2^21428749 is an apocalyptic number.

It is an amenable number.

21428749 is a deficient number, since it is larger than the sum of its proper divisors (498387).

21428749 is an equidigital number, since it uses as much as digits as its factorization.

21428749 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 498386.

The product of its digits is 32256, while the sum is 37.

The square root of 21428749 is about 4629.1196787294. The cubic root of 21428749 is about 277.7573793673.

The spelling of 21428749 in words is "twenty-one million, four hundred twenty-eight thousand, seven hundred forty-nine".