21216671 has 4 divisors (see below), whose sum is σ = 24247632. Its totient is φ = 18185712.

The previous prime is 21216659. The next prime is 21216707. The reversal of 21216671 is 17661212.

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 21216671 - 2⁶ = 21216607 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 21216671.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21216631) 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, 1515470 + ... + 1515483.

It is an arithmetic number, because the mean of its divisors is an integer number (6061908).

Almost surely, 2^21216671 is an apocalyptic number.

21216671 is a deficient number, since it is larger than the sum of its proper divisors (3030961).

21216671 is an equidigital number, since it uses as much as digits as its factorization.

21216671 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3030960.

The product of its digits is 1008, while the sum is 26.

The square root of 21216671 is about 4606.1557724419. The cubic root of 21216671 is about 276.8380282252.

Adding to 21216671 its reverse (17661212), we get a palindrome (38877883).

It can be divided in two parts, 2 and 1216671, that multiplied together give a palindrome (2433342).

The spelling of 21216671 in words is "twenty-one million, two hundred sixteen thousand, six hundred seventy-one".