21409591 has 8 divisors (see below), whose sum is σ = 24527360. Its totient is φ = 18306648.

The previous prime is 21409559. The next prime is 21409603. The reversal of 21409591 is 19590412.

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 21409591 - 2⁵ = 21409559 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21409501) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 411 + ... + 6556.

It is an arithmetic number, because the mean of its divisors is an integer number (3065920).

Almost surely, 2^21409591 is an apocalyptic number.

21409591 is a deficient number, since it is larger than the sum of its proper divisors (3117769).

21409591 is an equidigital number, since it uses as much as digits as its factorization.

21409591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7413.

The product of its (nonzero) digits is 3240, while the sum is 31.

The square root of 21409591 is about 4627.0499240877. The cubic root of 21409591 is about 277.6745799707.

It can be divided in two parts, 2 and 1409591, that multiplied together give a palindrome (2819182).

The spelling of 21409591 in words is "twenty-one million, four hundred nine thousand, five hundred ninety-one".