21503087 has 4 divisors (see below), whose sum is σ = 21632016. Its totient is φ = 21374160.

The previous prime is 21503071. The next prime is 21503093. The reversal of 21503087 is 78030512.

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 21503087 - 2⁴ = 21503071 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 (21503387) 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, 64214 + ... + 64547.

It is an arithmetic number, because the mean of its divisors is an integer number (5408004).

Almost surely, 2^21503087 is an apocalyptic number.

21503087 is a deficient number, since it is larger than the sum of its proper divisors (128929).

21503087 is a wasteful number, since it uses less digits than its factorization.

21503087 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128928.

The product of its (nonzero) digits is 1680, while the sum is 26.

The square root of 21503087 is about 4637.1421155708. The cubic root of 21503087 is about 278.0781960041.

Adding to 21503087 its reverse (78030512), we get a palindrome (99533599).

The spelling of 21503087 in words is "twenty-one million, five hundred three thousand, eighty-seven".