21217309 has 8 divisors (see below), whose sum is σ = 22524480. Its totient is φ = 19916736.

The previous prime is 21217307. The next prime is 21217337. The reversal of 21217309 is 90371212.

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 21217309 - 2¹ = 21217307 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 (21217307) 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, 6042 + ... + 8884.

It is an arithmetic number, because the mean of its divisors is an integer number (2815560).

Almost surely, 2^21217309 is an apocalyptic number.

It is an amenable number.

21217309 is a deficient number, since it is larger than the sum of its proper divisors (1307171).

21217309 is a wasteful number, since it uses less digits than its factorization.

21217309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3299.

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

The square root of 21217309 is about 4606.2250270693. The cubic root of 21217309 is about 276.8408031012.

The spelling of 21217309 in words is "twenty-one million, two hundred seventeen thousand, three hundred nine".