21645019 has 4 divisors (see below), whose sum is σ = 23612760. Its totient is φ = 19677280.

The previous prime is 21644969. The next prime is 21645023. The reversal of 21645019 is 91054612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21645019 - 2⁹ = 21644507 is a prime.

It is a super-2 number, since 2×21645019² = 937013695020722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21645059) 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, 983854 + ... + 983875.

It is an arithmetic number, because the mean of its divisors is an integer number (5903190).

Almost surely, 2^21645019 is an apocalyptic number.

21645019 is a deficient number, since it is larger than the sum of its proper divisors (1967741).

21645019 is a wasteful number, since it uses less digits than its factorization.

21645019 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1967740.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21645019 is about 4652.4207677294. The cubic root of 21645019 is about 278.6886769458.

The spelling of 21645019 in words is "twenty-one million, six hundred forty-five thousand, nineteen".