21599391 has 8 divisors (see below), whose sum is σ = 31417344. Its totient is φ = 13090520.

The previous prime is 21599381. The next prime is 21599399. The reversal of 21599391 is 19399512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21599391 - 2⁵ = 21599359 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21599399) 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 in 7 ways as a sum of consecutive naturals, for example, 327231 + ... + 327296.

It is an arithmetic number, because the mean of its divisors is an integer number (3927168).

Almost surely, 2^21599391 is an apocalyptic number.

21599391 is a deficient number, since it is larger than the sum of its proper divisors (9817953).

21599391 is a wasteful number, since it uses less digits than its factorization.

21599391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 654541.

The product of its digits is 21870, while the sum is 39.

The square root of 21599391 is about 4647.5144970188. The cubic root of 21599391 is about 278.4927126518.

The spelling of 21599391 in words is "twenty-one million, five hundred ninety-nine thousand, three hundred ninety-one".