21587387 has 4 divisors (see below), whose sum is σ = 21847560. Its totient is φ = 21327216.

The previous prime is 21587381. The next prime is 21587389. The reversal of 21587387 is 78378512.

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 21587387 - 2⁸ = 21587131 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21587381) 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, 129962 + ... + 130127.

It is an arithmetic number, because the mean of its divisors is an integer number (5461890).

Almost surely, 2^21587387 is an apocalyptic number.

21587387 is a deficient number, since it is larger than the sum of its proper divisors (260173).

21587387 is an equidigital number, since it uses as much as digits as its factorization.

21587387 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 260172.

The product of its digits is 94080, while the sum is 41.

The square root of 21587387 is about 4646.2228745509. Note that the first 3 decimals coincide. The cubic root of 21587387 is about 278.4411117214.

The spelling of 21587387 in words is "twenty-one million, five hundred eighty-seven thousand, three hundred eighty-seven".