21312778 has 16 divisors (see below), whose sum is σ = 33137280. Its totient is φ = 10273536.

The previous prime is 21312763. The next prime is 21312787. The reversal of 21312778 is 87721312.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5226 + ... + 8362.

It is an arithmetic number, because the mean of its divisors is an integer number (2071080).

Almost surely, 2^21312778 is an apocalyptic number.

21312778 is a deficient number, since it is larger than the sum of its proper divisors (11824502).

21312778 is a wasteful number, since it uses less digits than its factorization.

21312778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3261.

The product of its digits is 4704, while the sum is 31.

The square root of 21312778 is about 4616.5764371447. The cubic root of 21312778 is about 277.2554044148.

The spelling of 21312778 in words is "twenty-one million, three hundred twelve thousand, seven hundred seventy-eight".