21031331 has 4 divisors (see below), whose sum is σ = 21239664. Its totient is φ = 20823000.

The previous prime is 21031313. The next prime is 21031333. The reversal of 21031331 is 13313012.

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

It is a cyclic number.

It is not a de Polignac number, because 21031331 - 2²² = 16837027 is a prime.

It is a super-2 number, since 2×21031331² = 884633767263122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21031333) 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, 104015 + ... + 104216.

It is an arithmetic number, because the mean of its divisors is an integer number (5309916).

Almost surely, 2^21031331 is an apocalyptic number.

21031331 is a deficient number, since it is larger than the sum of its proper divisors (208333).

21031331 is a wasteful number, since it uses less digits than its factorization.

21031331 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 208332.

The product of its (nonzero) digits is 54, while the sum is 14.

The square root of 21031331 is about 4585.9929132087. The cubic root of 21031331 is about 276.0295555761.

Adding to 21031331 its reverse (13313012), we get a palindrome (34344343).

The spelling of 21031331 in words is "twenty-one million, thirty-one thousand, three hundred thirty-one".