21117517 has 4 divisors (see below), whose sum is σ = 21132700. Its totient is φ = 21102336.

The previous prime is 21117487. The next prime is 21117521. The reversal of 21117517 is 71571112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11062276 + 10055241 = 3326^2 + 3171^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21117517 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21117491 and 21117500.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21117557) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5268 + ... + 8365.

It is an arithmetic number, because the mean of its divisors is an integer number (5283175).

Almost surely, 2^21117517 is an apocalyptic number.

It is an amenable number.

21117517 is a deficient number, since it is larger than the sum of its proper divisors (15183).

21117517 is a wasteful number, since it uses less digits than its factorization.

21117517 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15182.

The product of its digits is 490, while the sum is 25.

The square root of 21117517 is about 4595.3799625276. The cubic root of 21117517 is about 276.4060963385.

Adding to 21117517 its reverse (71571112), we get a palindrome (92688629).

The spelling of 21117517 in words is "twenty-one million, one hundred seventeen thousand, five hundred seventeen".