21406013 has 4 divisors (see below), whose sum is σ = 21646620. Its totient is φ = 21165408.

The previous prime is 21406001. The next prime is 21406037. The reversal of 21406013 is 31060412.

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 5189284 + 16216729 = 2278^2 + 4027^2 .

It is a cyclic number.

It is not a de Polignac number, because 21406013 - 2⁴ = 21405997 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21405982 and 21406000.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21402013) 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, 120170 + ... + 120347.

It is an arithmetic number, because the mean of its divisors is an integer number (5411655).

Almost surely, 2^21406013 is an apocalyptic number.

It is an amenable number.

21406013 is a deficient number, since it is larger than the sum of its proper divisors (240607).

21406013 is an equidigital number, since it uses as much as digits as its factorization.

21406013 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 240606.

The product of its (nonzero) digits is 144, while the sum is 17.

The square root of 21406013 is about 4626.6632684906. The cubic root of 21406013 is about 277.6591106576.

Adding to 21406013 its reverse (31060412), we get a palindrome (52466425).

The spelling of 21406013 in words is "twenty-one million, four hundred six thousand, thirteen".