21216667 has 4 divisors (see below), whose sum is σ = 21227536. Its totient is φ = 21205800.

The previous prime is 21216659. The next prime is 21216707. The reversal of 21216667 is 76661212.

It is a happy number.

21216667 is nontrivially palindromic in base 13.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21216667 - 2³ = 21216659 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21216607) 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, 1608 + ... + 6709.

It is an arithmetic number, because the mean of its divisors is an integer number (5306884).

Almost surely, 2^21216667 is an apocalyptic number.

21216667 is a deficient number, since it is larger than the sum of its proper divisors (10869).

21216667 is an equidigital number, since it uses as much as digits as its factorization.

21216667 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10868.

The product of its digits is 6048, while the sum is 31.

The square root of 21216667 is about 4606.1553382403. The cubic root of 21216667 is about 276.8380108277.

Adding to 21216667 its reverse (76661212), we get a palindrome (97877879).

The spelling of 21216667 in words is "twenty-one million, two hundred sixteen thousand, six hundred sixty-seven".