21216688615 has 4 divisors (see below), whose sum is σ = 25460026344. Its totient is φ = 16973350888.

The previous prime is 21216688613. The next prime is 21216688657. The reversal of 21216688615 is 51688661212.

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 21216688615 - 2¹ = 21216688613 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216688613) 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, 2121668857 + ... + 2121668866.

It is an arithmetic number, because the mean of its divisors is an integer number (6365006586).

Almost surely, 2^21216688615 is an apocalyptic number.

21216688615 is a deficient number, since it is larger than the sum of its proper divisors (4243337729).

21216688615 is an equidigital number, since it uses as much as digits as its factorization.

21216688615 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4243337728.

The product of its digits is 276480, while the sum is 46.

The spelling of 21216688615 in words is "twenty-one billion, two hundred sixteen million, six hundred eighty-eight thousand, six hundred fifteen".