21049813 has 2 divisors, whose sum is σ = 21049814. Its totient is φ = 21049812.

The previous prime is 21049811. The next prime is 21049817. The reversal of 21049813 is 31894012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19554084 + 1495729 = 4422^2 + 1223^2 .

It is a cyclic number.

It is not a de Polignac number, because 21049813 - 2¹ = 21049811 is a prime.

Together with 21049811, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21049811) 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 as a sum of consecutive naturals, namely, 10524906 + 10524907.

It is an arithmetic number, because the mean of its divisors is an integer number (10524907).

Almost surely, 2^21049813 is an apocalyptic number.

It is an amenable number.

21049813 is a deficient number, since it is larger than the sum of its proper divisors (1).

21049813 is an equidigital number, since it uses as much as digits as its factorization.

21049813 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1728, while the sum is 28.

The square root of 21049813 is about 4588.0075196102. The cubic root of 21049813 is about 276.1103887004.

The spelling of 21049813 in words is "twenty-one million, forty-nine thousand, eight hundred thirteen".