21031 has 2 divisors, whose sum is σ = 21032. Its totient is φ = 21030.

The previous prime is 21023. The next prime is 21059. The reversal of 21031 is 13012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21031 - 2³ = 21023 is a prime.

It is a super-2 number, since 2×21031² = 884605922, which contains 22 as substring.

It is a plaindrome in base 11.

It is a zygodrome in base 5.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10515 + 10516.

It is an arithmetic number, because the mean of its divisors is an integer number (10516).

2²¹⁰³¹ is an apocalyptic number.

21031 is a deficient number, since it is larger than the sum of its proper divisors (1).

21031 is an equidigital number, since it uses as much as digits as its factorization.

21031 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21031 is about 145.0206881793. The cubic root of 21031 is about 27.6028107478.

Adding to 21031 its reverse (13012), we get a palindrome (34043).

The spelling of 21031 in words is "twenty-one thousand, thirty-one".