21709213 has 8 divisors (see below), whose sum is σ = 22329216. Its totient is φ = 21093600.

The previous prime is 21709211. The next prime is 21709271. The reversal of 21709213 is 31290712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21709213 - 2¹ = 21709211 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 (21709211) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10668 + ... + 12538.

It is an arithmetic number, because the mean of its divisors is an integer number (2791152).

Almost surely, 2^21709213 is an apocalyptic number.

It is an amenable number.

21709213 is a deficient number, since it is larger than the sum of its proper divisors (620003).

21709213 is a wasteful number, since it uses less digits than its factorization.

21709213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2195.

The product of its (nonzero) digits is 756, while the sum is 25.

The square root of 21709213 is about 4659.3146491732. The cubic root of 21709213 is about 278.9639132336.

Adding to 21709213 its reverse (31290712), we get a palindrome (52999925).

The spelling of 21709213 in words is "twenty-one million, seven hundred nine thousand, two hundred thirteen".