21056513 has 4 divisors (see below), whose sum is σ = 21135060. Its totient is φ = 20977968.

The previous prime is 21056507. The next prime is 21056527. The reversal of 21056513 is 31565012.

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 734449 + 20322064 = 857^2 + 4508^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21056513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21056543) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 38870 + ... + 39407.

It is an arithmetic number, because the mean of its divisors is an integer number (5283765).

Almost surely, 2^21056513 is an apocalyptic number.

It is an amenable number.

21056513 is a deficient number, since it is larger than the sum of its proper divisors (78547).

21056513 is an equidigital number, since it uses as much as digits as its factorization.

21056513 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78546.

The product of its (nonzero) digits is 900, while the sum is 23.

The square root of 21056513 is about 4588.7376259708. The cubic root of 21056513 is about 276.1396802253.

The spelling of 21056513 in words is "twenty-one million, fifty-six thousand, five hundred thirteen".