21311645 has 4 divisors (see below), whose sum is σ = 25573980. Its totient is φ = 17049312.

The previous prime is 21311629. The next prime is 21311683. The reversal of 21311645 is 54611312.

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 13853284 + 7458361 = 3722^2 + 2731^2 .

It is a cyclic number.

It is not a de Polignac number, because 21311645 - 2⁴ = 21311629 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21311645.

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 2131160 + ... + 2131169.

It is an arithmetic number, because the mean of its divisors is an integer number (6393495).

Almost surely, 2^21311645 is an apocalyptic number.

It is an amenable number.

21311645 is a deficient number, since it is larger than the sum of its proper divisors (4262335).

21311645 is an equidigital number, since it uses as much as digits as its factorization.

21311645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4262334.

The product of its digits is 720, while the sum is 23.

The square root of 21311645 is about 4616.4537255344. The cubic root of 21311645 is about 277.2504913068.

Adding to 21311645 its reverse (54611312), we get a palindrome (75922957).

The spelling of 21311645 in words is "twenty-one million, three hundred eleven thousand, six hundred forty-five".