21591893 has 2 divisors, whose sum is σ = 21591894. Its totient is φ = 21591892.

The previous prime is 21591839. The next prime is 21591907. The reversal of 21591893 is 39819512.

Together with previous prime (21591839) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16826404 + 4765489 = 4102^2 + 2183^2 .

It is a cyclic number.

It is not a de Polignac number, because 21591893 - 2¹⁶ = 21526357 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21591833) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10795946 + 10795947.

It is an arithmetic number, because the mean of its divisors is an integer number (10795947).

Almost surely, 2^21591893 is an apocalyptic number.

It is an amenable number.

21591893 is a deficient number, since it is larger than the sum of its proper divisors (1).

21591893 is an equidigital number, since it uses as much as digits as its factorization.

21591893 is an evil number, because the sum of its binary digits is even.

The product of its digits is 19440, while the sum is 38.

The square root of 21591893 is about 4646.7077592635. The cubic root of 21591893 is about 278.4604836562.

The spelling of 21591893 in words is "twenty-one million, five hundred ninety-one thousand, eight hundred ninety-three".