21000013 has 4 divisors (see below), whose sum is σ = 21013020. Its totient is φ = 20987008.

The previous prime is 20999999. The next prime is 21000037. The reversal of 21000013 is 31000012.

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

It can be written as a sum of positive squares in 2 ways, for example, as 5774409 + 15225604 = 2403^2 + 3902^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000013 - 2¹⁷ = 20868941 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000313) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3670 + ... + 7447.

It is an arithmetic number, because the mean of its divisors is an integer number (5253255).

Almost surely, 2^21000013 is an apocalyptic number.

It is an amenable number.

21000013 is a deficient number, since it is larger than the sum of its proper divisors (13007).

21000013 is a wasteful number, since it uses less digits than its factorization.

21000013 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13006.

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

The square root of 21000013 is about 4582.5771133719. The cubic root of 21000013 is about 275.8924745683.

Adding to 21000013 its reverse (31000012), we get a palindrome (52000025).

Subtracting 21000013 from its reverse (31000012), we obtain a palindrome (9999999).

The spelling of 21000013 in words is "twenty-one million, thirteen", and thus it is an aban number and an uban number.