21644091 has 40 divisors (see below), whose sum is σ = 37635840. Its totient is φ = 12139632.

The previous prime is 21644089. The next prime is 21644099. The reversal of 21644091 is 19044612.

21644091 is a `hidden beast` number, since 216 + 440 + 9 + 1 = 666.

It is not a de Polignac number, because 21644091 - 2¹ = 21644089 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21644099) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 33130 + ... + 33776.

It is an arithmetic number, because the mean of its divisors is an integer number (940896).

Almost surely, 2^21644091 is an apocalyptic number.

21644091 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21644091 is a deficient number, since it is larger than the sum of its proper divisors (15991749).

21644091 is an equidigital number, since it uses as much as digits as its factorization.

21644091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 725 (or 716 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21644091 is about 4652.3210336347. The cubic root of 21644091 is about 278.6846940928.

The spelling of 21644091 in words is "twenty-one million, six hundred forty-four thousand, ninety-one".