21671813 has 2 divisors, whose sum is σ = 21671814. Its totient is φ = 21671812.

The previous prime is 21671801. The next prime is 21671831. The reversal of 21671813 is 31817612.

Together with next prime (21671831) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19731364 + 1940449 = 4442^2 + 1393^2 .

It is a cyclic number.

It is not a de Polignac number, because 21671813 - 2⁸ = 21671557 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21671863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10835906 + 10835907.

It is an arithmetic number, because the mean of its divisors is an integer number (10835907).

Almost surely, 2^21671813 is an apocalyptic number.

It is an amenable number.

21671813 is a deficient number, since it is larger than the sum of its proper divisors (1).

21671813 is an equidigital number, since it uses as much as digits as its factorization.

21671813 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 29.

The square root of 21671813 is about 4655.2994533112. The cubic root of 21671813 is about 278.8036241824.

The spelling of 21671813 in words is "twenty-one million, six hundred seventy-one thousand, eight hundred thirteen".