21890645 has 16 divisors (see below), whose sum is σ = 31788288. Its totient is φ = 14127360.

The previous prime is 21890629. The next prime is 21890647. The reversal of 21890645 is 54609812.

It is not a de Polignac number, because 21890645 - 2⁴ = 21890629 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (35).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21890647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17801 + ... + 18990.

It is an arithmetic number, because the mean of its divisors is an integer number (1986768).

Almost surely, 2^21890645 is an apocalyptic number.

It is an amenable number.

21890645 is a deficient number, since it is larger than the sum of its proper divisors (9897643).

21890645 is a wasteful number, since it uses less digits than its factorization.

21890645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36820.

The product of its (nonzero) digits is 17280, while the sum is 35.

The square root of 21890645 is about 4678.7439553795. The cubic root of 21890645 is about 279.7388934926.

The spelling of 21890645 in words is "twenty-one million, eight hundred ninety thousand, six hundred forty-five".