21216715 has 16 divisors (see below), whose sum is σ = 27873216. Its totient is φ = 15408000.

The previous prime is 21216707. The next prime is 21216737. The reversal of 21216715 is 51761212.

It is not a de Polignac number, because 21216715 - 2³ = 21216707 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21216715.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1290 + ... + 6640.

It is an arithmetic number, because the mean of its divisors is an integer number (1742076).

Almost surely, 2^21216715 is an apocalyptic number.

21216715 is a deficient number, since it is larger than the sum of its proper divisors (6656501).

21216715 is a wasteful number, since it uses less digits than its factorization.

21216715 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5430.

The product of its digits is 840, while the sum is 25.

The square root of 21216715 is about 4606.1605486565. The cubic root of 21216715 is about 276.8382195978.

Adding to 21216715 its reverse (51761212), we get a palindrome (72977927).

It can be divided in two parts, 2121 and 6715, that added together give a square (8836 = 94²).

The spelling of 21216715 in words is "twenty-one million, two hundred sixteen thousand, seven hundred fifteen".