21716221 has 4 divisors (see below), whose sum is σ = 22859200. Its totient is φ = 20573244.

The previous prime is 21716159. The next prime is 21716237. The reversal of 21716221 is 12261712.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21716221 - 2⁹ = 21715709 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 12.

It is a junction number, because it is equal to n+sod(n) for n = 21716192 and 21716201.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21716251) 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, 571461 + ... + 571498.

It is an arithmetic number, because the mean of its divisors is an integer number (5714800).

Almost surely, 2^21716221 is an apocalyptic number.

It is an amenable number.

21716221 is a deficient number, since it is larger than the sum of its proper divisors (1142979).

21716221 is a wasteful number, since it uses less digits than its factorization.

21716221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1142978.

The product of its digits is 336, while the sum is 22.

The square root of 21716221 is about 4660.0666304249. The cubic root of 21716221 is about 278.9939276608.

Adding to 21716221 its reverse (12261712), we get a palindrome (33977933).

The spelling of 21716221 in words is "twenty-one million, seven hundred sixteen thousand, two hundred twenty-one".