21217009 has 16 divisors (see below), whose sum is σ = 24131520. Its totient is φ = 18477760.

The previous prime is 21216997. The next prime is 21217019. The reversal of 21217009 is 90071212.

It is a cyclic number.

It is not a de Polignac number, because 21217009 - 2⁹ = 21216497 is a prime.

It is a super-2 number, since 2×21217009² = 900322941812162, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21217019) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 72267 + ... + 72559.

It is an arithmetic number, because the mean of its divisors is an integer number (1508220).

Almost surely, 2^21217009 is an apocalyptic number.

21217009 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21217009 is a deficient number, since it is larger than the sum of its proper divisors (2914511).

21217009 is a wasteful number, since it uses less digits than its factorization.

21217009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 560.

The product of its (nonzero) digits is 252, while the sum is 22.

The square root of 21217009 is about 4606.1924623272. The cubic root of 21217009 is about 276.8394983075.

The spelling of 21217009 in words is "twenty-one million, two hundred seventeen thousand, nine".