21287858 has 4 divisors (see below), whose sum is σ = 31931790. Its totient is φ = 10643928.

The previous prime is 21287837. The next prime is 21287869. The reversal of 21287858 is 85878212.

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

It can be written as a sum of positive squares in only one way, i.e., 13741849 + 7546009 = 3707^2 + 2747^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5321963 + ... + 5321966.

Almost surely, 2^21287858 is an apocalyptic number.

21287858 is a deficient number, since it is larger than the sum of its proper divisors (10643932).

21287858 is a wasteful number, since it uses less digits than its factorization.

21287858 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10643931.

The product of its digits is 71680, while the sum is 41.

The square root of 21287858 is about 4613.8766780225. The cubic root of 21287858 is about 277.1473018281.

The spelling of 21287858 in words is "twenty-one million, two hundred eighty-seven thousand, eight hundred fifty-eight".