21520013 has 2 divisors, whose sum is σ = 21520014. Its totient is φ = 21520012.

The previous prime is 21520003. The next prime is 21520021. The reversal of 21520013 is 31002512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15697444 + 5822569 = 3962^2 + 2413^2 .

It is a cyclic number.

It is not a de Polignac number, because 21520013 - 2¹² = 21515917 is a prime.

It is a super-2 number, since 2×21520013² = 926221919040338, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21520013.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21520003) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10760006 + 10760007.

It is an arithmetic number, because the mean of its divisors is an integer number (10760007).

Almost surely, 2^21520013 is an apocalyptic number.

It is an amenable number.

21520013 is a deficient number, since it is larger than the sum of its proper divisors (1).

21520013 is an equidigital number, since it uses as much as digits as its factorization.

21520013 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 60, while the sum is 14.

The square root of 21520013 is about 4638.9668030716. The cubic root of 21520013 is about 278.1511392846.

Adding to 21520013 its reverse (31002512), we get a palindrome (52522525).

The spelling of 21520013 in words is "twenty-one million, five hundred twenty thousand, thirteen".