21718031 has 4 divisors (see below), whose sum is σ = 21761712. Its totient is φ = 21674352.

The previous prime is 21717989. The next prime is 21718033. The reversal of 21718031 is 13081712.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21718031 is a prime.

It is a super-2 number, since 2×21718031² = 943345741033922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21717988 and 21718006.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21718033) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21086 + ... + 22091.

It is an arithmetic number, because the mean of its divisors is an integer number (5440428).

Almost surely, 2^21718031 is an apocalyptic number.

21718031 is a deficient number, since it is larger than the sum of its proper divisors (43681).

21718031 is an equidigital number, since it uses as much as digits as its factorization.

21718031 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43680.

The product of its (nonzero) digits is 336, while the sum is 23.

The square root of 21718031 is about 4660.2608296103. The cubic root of 21718031 is about 279.0016786254.

Adding to 21718031 its reverse (13081712), we get a palindrome (34799743).

The spelling of 21718031 in words is "twenty-one million, seven hundred eighteen thousand, thirty-one".