21312663 has 4 divisors (see below), whose sum is σ = 28416888. Its totient is φ = 14208440.

The previous prime is 21312647. The next prime is 21312671. The reversal of 21312663 is 36621312.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21312663 - 2⁴ = 21312647 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21312673) 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, 3552108 + ... + 3552113.

It is an arithmetic number, because the mean of its divisors is an integer number (7104222).

Almost surely, 2^21312663 is an apocalyptic number.

21312663 is a deficient number, since it is larger than the sum of its proper divisors (7104225).

21312663 is an equidigital number, since it uses as much as digits as its factorization.

21312663 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7104224.

The product of its digits is 1296, while the sum is 24.

The square root of 21312663 is about 4616.5639820109. The cubic root of 21312663 is about 277.2549057401.

Adding to 21312663 its reverse (36621312), we get a palindrome (57933975).

The spelling of 21312663 in words is "twenty-one million, three hundred twelve thousand, six hundred sixty-three".