21087907 has 4 divisors (see below), whose sum is σ = 21104640. Its totient is φ = 21071176.

The previous prime is 21087889. The next prime is 21087917. The reversal of 21087907 is 70978012.

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 21087907 - 2⁷ = 21087779 is a prime.

It is a super-3 number, since 3×21087907³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21087917) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6307 + ... + 9052.

It is an arithmetic number, because the mean of its divisors is an integer number (5276160).

Almost surely, 2^21087907 is an apocalyptic number.

21087907 is a deficient number, since it is larger than the sum of its proper divisors (16733).

21087907 is a wasteful number, since it uses less digits than its factorization.

21087907 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16732.

The product of its (nonzero) digits is 7056, while the sum is 34.

The square root of 21087907 is about 4592.1571183922. The cubic root of 21087907 is about 276.2768479875.

The spelling of 21087907 in words is "twenty-one million, eighty-seven thousand, nine hundred seven".