21645861 has 16 divisors (see below), whose sum is σ = 30369600. Its totient is φ = 13693568.

The previous prime is 21645859. The next prime is 21645881. The reversal of 21645861 is 16854612.

It is not a de Polignac number, because 21645861 - 2¹ = 21645859 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21645881) 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, 3025 + ... + 7241.

It is an arithmetic number, because the mean of its divisors is an integer number (1898100).

Almost surely, 2^21645861 is an apocalyptic number.

It is an amenable number.

21645861 is a deficient number, since it is larger than the sum of its proper divisors (8723739).

21645861 is a wasteful number, since it uses less digits than its factorization.

21645861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4308.

The product of its digits is 11520, while the sum is 33.

The square root of 21645861 is about 4652.5112573749. The cubic root of 21645861 is about 278.6922905998.

The spelling of 21645861 in words is "twenty-one million, six hundred forty-five thousand, eight hundred sixty-one".