21591017 has 12 divisors (see below), whose sum is σ = 25797060. Its totient is φ = 18004896.

The previous prime is 21591007. The next prime is 21591019. The reversal of 21591017 is 71019512.

It can be written as a sum of positive squares in 2 ways, for example, as 13868176 + 7722841 = 3724^2 + 2779^2 .

It is not a de Polignac number, because 21591017 - 2⁶ = 21590953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21591019) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4142 + ... + 7767.

It is an arithmetic number, because the mean of its divisors is an integer number (2149755).

Almost surely, 2^21591017 is an apocalyptic number.

It is an amenable number.

21591017 is a deficient number, since it is larger than the sum of its proper divisors (4206043).

21591017 is a wasteful number, since it uses less digits than its factorization.

21591017 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11960 (or 11953 counting only the distinct ones).

The product of its (nonzero) digits is 630, while the sum is 26.

The square root of 21591017 is about 4646.6134980220. The cubic root of 21591017 is about 278.4567178187.

The spelling of 21591017 in words is "twenty-one million, five hundred ninety-one thousand, seventeen".