21001331 has 4 divisors (see below), whose sum is σ = 22616832. Its totient is φ = 19385832.

The previous prime is 21001319. The next prime is 21001349. The reversal of 21001331 is 13310012.

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 21001331 - 2¹⁰ = 21000307 is a prime.

It is a super-2 number, since 2×21001331² = 882111807543122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21001381) 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, 807731 + ... + 807756.

It is an arithmetic number, because the mean of its divisors is an integer number (5654208).

Almost surely, 2^21001331 is an apocalyptic number.

21001331 is a deficient number, since it is larger than the sum of its proper divisors (1615501).

21001331 is a wasteful number, since it uses less digits than its factorization.

21001331 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1615500.

The product of its (nonzero) digits is 18, while the sum is 11.

The square root of 21001331 is about 4582.7209166608. The cubic root of 21001331 is about 275.8982462897.

Adding to 21001331 its reverse (13310012), we get a palindrome (34311343).

The spelling of 21001331 in words is "twenty-one million, one thousand, three hundred thirty-one".