21500217 has 6 divisors (see below), whose sum is σ = 31055882. Its totient is φ = 14333472.

The previous prime is 21500209. The next prime is 21500231. The reversal of 21500217 is 71200512.

It can be written as a sum of positive squares in only one way, i.e., 13682601 + 7817616 = 3699^2 + 2796^2 .

It is not a de Polignac number, because 21500217 - 2³ = 21500209 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 21500217.

It is not an unprimeable number, because it can be changed into a prime (21507217) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1194448 + ... + 1194465.

Almost surely, 2^21500217 is an apocalyptic number.

It is an amenable number.

21500217 is a deficient number, since it is larger than the sum of its proper divisors (9555665).

21500217 is a wasteful number, since it uses less digits than its factorization.

21500217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2388919 (or 2388916 counting only the distinct ones).

The product of its (nonzero) digits is 140, while the sum is 18.

The square root of 21500217 is about 4636.8326474006. The cubic root of 21500217 is about 278.0658238280.

Adding to 21500217 its reverse (71200512), we get a palindrome (92700729).

The spelling of 21500217 in words is "twenty-one million, five hundred thousand, two hundred seventeen".