21000031 has 16 divisors (see below), whose sum is σ = 23859360. Its totient is φ = 18345600.

The previous prime is 20999999. The next prime is 21000037. The reversal of 21000031 is 13000012.

It is not a de Polignac number, because 21000031 - 2⁵ = 20999999 is a prime.

It is a super-2 number, since 2×21000031² = 882002604001922, 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 = 20999978 and 21000023.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000037) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19456 + ... + 20506.

It is an arithmetic number, because the mean of its divisors is an integer number (1491210).

Almost surely, 2^21000031 is an apocalyptic number.

21000031 is a deficient number, since it is larger than the sum of its proper divisors (2859329).

21000031 is a wasteful number, since it uses less digits than its factorization.

21000031 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1146.

The product of its (nonzero) digits is 6, while the sum is 7.

The square root of 21000031 is about 4582.5790773319. The cubic root of 21000031 is about 275.8925533946.

Adding to 21000031 its reverse (13000012), we get a palindrome (34000043).

The spelling of 21000031 in words is "twenty-one million, thirty-one", and thus it is an aban number and an uban number.