21207878 has 4 divisors (see below), whose sum is σ = 31811820. Its totient is φ = 10603938.

The previous prime is 21207869. The next prime is 21207881. The reversal of 21207878 is 87870212.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5301968 + ... + 5301971.

It is an arithmetic number, because the mean of its divisors is an integer number (7952955).

Almost surely, 2^21207878 is an apocalyptic number.

21207878 is a deficient number, since it is larger than the sum of its proper divisors (10603942).

21207878 is a wasteful number, since it uses less digits than its factorization.

21207878 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10603941.

The product of its (nonzero) digits is 12544, while the sum is 35.

The square root of 21207878 is about 4605.2011899590. The cubic root of 21207878 is about 276.7997788514.

The spelling of 21207878 in words is "twenty-one million, two hundred seven thousand, eight hundred seventy-eight".