21591839 has 2 divisors, whose sum is σ = 21591840. Its totient is φ = 21591838.

The previous prime is 21591833. The next prime is 21591893. The reversal of 21591839 is 93819512.

Together with next prime (21591893) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21591839 - 2¹⁶ = 21526303 is a prime.

It is a super-2 number, since 2×21591839² = 932415022803842, which contains 22 as substring.

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, 10795919 + 10795920.

It is an arithmetic number, because the mean of its divisors is an integer number (10795920).

Almost surely, 2^21591839 is an apocalyptic number.

21591839 is a deficient number, since it is larger than the sum of its proper divisors (1).

21591839 is an equidigital number, since it uses as much as digits as its factorization.

21591839 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21591839 is about 4646.7019486944. The cubic root of 21591839 is about 278.4602515185.

The spelling of 21591839 in words is "twenty-one million, five hundred ninety-one thousand, eight hundred thirty-nine".