21555645 has 16 divisors (see below), whose sum is σ = 35422080. Its totient is φ = 11185344.

The previous prime is 21555637. The next prime is 21555647. The reversal of 21555645 is 54655512.

It is not a de Polignac number, because 21555645 - 2³ = 21555637 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21555647) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 18865 + ... + 19974.

It is an arithmetic number, because the mean of its divisors is an integer number (2213880).

Almost surely, 2^21555645 is an apocalyptic number.

It is an amenable number.

21555645 is a deficient number, since it is larger than the sum of its proper divisors (13866435).

21555645 is a wasteful number, since it uses less digits than its factorization.

21555645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38884.

The product of its digits is 30000, while the sum is 33.

The square root of 21555645 is about 4642.8057249900. The cubic root of 21555645 is about 278.3045719102.

The spelling of 21555645 in words is "twenty-one million, five hundred fifty-five thousand, six hundred forty-five".