21172813 has 8 divisors (see below), whose sum is σ = 22413600. Its totient is φ = 19966128.

The previous prime is 21172807. The next prime is 21172819. The reversal of 21172813 is 31827112.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21172807) and next prime (21172819).

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21172813 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 (21172819) 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, 7243 + ... + 9736.

It is an arithmetic number, because the mean of its divisors is an integer number (2801700).

Almost surely, 2^21172813 is an apocalyptic number.

It is an amenable number.

21172813 is a deficient number, since it is larger than the sum of its proper divisors (1240787).

21172813 is a wasteful number, since it uses less digits than its factorization.

21172813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17051.

The product of its digits is 672, while the sum is 25.

The square root of 21172813 is about 4601.3925066223. The cubic root of 21172813 is about 276.6471415714.

Adding to 21172813 its reverse (31827112), we get a palindrome (52999925).

The spelling of 21172813 in words is "twenty-one million, one hundred seventy-two thousand, eight hundred thirteen".