21001031 has 4 divisors (see below), whose sum is σ = 21209064. Its totient is φ = 20793000.

The previous prime is 21001021. The next prime is 21001033. The reversal of 21001031 is 13010012.

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-21001031 is a prime.

It is a super-2 number, since 2×21001031² = 882086606125922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001033) 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, 103865 + ... + 104066.

It is an arithmetic number, because the mean of its divisors is an integer number (5302266).

Almost surely, 2^21001031 is an apocalyptic number.

21001031 is a deficient number, since it is larger than the sum of its proper divisors (208033).

21001031 is a wasteful number, since it uses less digits than its factorization.

21001031 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 208032.

The product of its (nonzero) digits is 6, while the sum is 8.

The square root of 21001031 is about 4582.6881848976. The cubic root of 21001031 is about 275.8969325655.

Adding to 21001031 its reverse (13010012), we get a palindrome (34011043).

The spelling of 21001031 in words is "twenty-one million, one thousand, thirty-one".