21117865 has 8 divisors (see below), whose sum is σ = 25527240. Its totient is φ = 16770432.

The previous prime is 21117847. The next prime is 21117869. The reversal of 21117865 is 56871112.

It can be written as a sum of positive squares in 4 ways, for example, as 6471936 + 14645929 = 2544^2 + 3827^2 .

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 21117865 - 2⁷ = 21117737 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21117869) 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, 14730 + ... + 16099.

It is an arithmetic number, because the mean of its divisors is an integer number (3190905).

Almost surely, 2^21117865 is an apocalyptic number.

It is an amenable number.

21117865 is a deficient number, since it is larger than the sum of its proper divisors (4409375).

21117865 is a wasteful number, since it uses less digits than its factorization.

21117865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30971.

The product of its digits is 3360, while the sum is 31.

The square root of 21117865 is about 4595.4178264876. The cubic root of 21117865 is about 276.4076146482.

Adding to 21117865 its reverse (56871112), we get a palindrome (77988977).

The spelling of 21117865 in words is "twenty-one million, one hundred seventeen thousand, eight hundred sixty-five".