21331645 has 4 divisors (see below), whose sum is σ = 25597980. Its totient is φ = 17065312.

The previous prime is 21331643. The next prime is 21331657. The reversal of 21331645 is 54613312.

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

It can be written as a sum of positive squares in 2 ways, for example, as 3175524 + 18156121 = 1782^2 + 4261^2 .

It is a cyclic number.

It is not a de Polignac number, because 21331645 - 2¹ = 21331643 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21331643) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2133160 + ... + 2133169.

It is an arithmetic number, because the mean of its divisors is an integer number (6399495).

Almost surely, 2^21331645 is an apocalyptic number.

It is an amenable number.

21331645 is a deficient number, since it is larger than the sum of its proper divisors (4266335).

21331645 is an equidigital number, since it uses as much as digits as its factorization.

21331645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4266334.

The product of its digits is 2160, while the sum is 25.

The square root of 21331645 is about 4618.6193824562. The cubic root of 21331645 is about 277.3371931413.

Adding to 21331645 its reverse (54613312), we get a palindrome (75944957).

The spelling of 21331645 in words is "twenty-one million, three hundred thirty-one thousand, six hundred forty-five".