21321687 has 4 divisors (see below), whose sum is σ = 28428920. Its totient is φ = 14214456.

The previous prime is 21321683. The next prime is 21321709. The reversal of 21321687 is 78612312.

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

It is not a de Polignac number, because 21321687 - 2² = 21321683 is a prime.

It is a super-2 number, since 2×21321687² = 909228673051938, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21321683) 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, 3553612 + ... + 3553617.

It is an arithmetic number, because the mean of its divisors is an integer number (7107230).

Almost surely, 2^21321687 is an apocalyptic number.

21321687 is a deficient number, since it is larger than the sum of its proper divisors (7107233).

21321687 is an equidigital number, since it uses as much as digits as its factorization.

21321687 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7107232.

The product of its digits is 4032, while the sum is 30.

The square root of 21321687 is about 4617.5412288360. The cubic root of 21321687 is about 277.2940310751.

Adding to 21321687 its reverse (78612312), we get a palindrome (99933999).

The spelling of 21321687 in words is "twenty-one million, three hundred twenty-one thousand, six hundred eighty-seven".