21431087 has 4 divisors (see below), whose sum is σ = 22170120. Its totient is φ = 20692056.

The previous prime is 21431063. The next prime is 21431099. The reversal of 21431087 is 78013412.

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 21431087 - 2⁶ = 21431023 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21431017) 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, 369473 + ... + 369530.

It is an arithmetic number, because the mean of its divisors is an integer number (5542530).

Almost surely, 2^21431087 is an apocalyptic number.

21431087 is a deficient number, since it is larger than the sum of its proper divisors (739033).

21431087 is an equidigital number, since it uses as much as digits as its factorization.

21431087 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 739032.

The product of its (nonzero) digits is 1344, while the sum is 26.

The square root of 21431087 is about 4629.3722036579. The cubic root of 21431087 is about 277.7674806435.

Adding to 21431087 its reverse (78013412), we get a palindrome (99444499).

The spelling of 21431087 in words is "twenty-one million, four hundred thirty-one thousand, eighty-seven".