21654391 has 4 divisors (see below), whose sum is σ = 23622984. Its totient is φ = 19685800.

The previous prime is 21654383. The next prime is 21654419. The reversal of 21654391 is 19345612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21654391 - 2³ = 21654383 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21654301) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 984280 + ... + 984301.

It is an arithmetic number, because the mean of its divisors is an integer number (5905746).

Almost surely, 2^21654391 is an apocalyptic number.

21654391 is a deficient number, since it is larger than the sum of its proper divisors (1968593).

21654391 is a wasteful number, since it uses less digits than its factorization.

21654391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1968592.

The product of its digits is 6480, while the sum is 31.

The square root of 21654391 is about 4653.4278763080. The cubic root of 21654391 is about 278.7288939492.

It can be divided in two parts, 2165 and 4391, that added together give a palindrome (6556).

The spelling of 21654391 in words is "twenty-one million, six hundred fifty-four thousand, three hundred ninety-one".