21153921 has 8 divisors (see below), whose sum is σ = 28368960. Its totient is φ = 14020752.

The previous prime is 21153917. The next prime is 21153929. The reversal of 21153921 is 12935112.

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

It is not a de Polignac number, because 21153921 - 2² = 21153917 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21153891 and 21153900.

It is not an unprimeable number, because it can be changed into a prime (21153929) 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, 19861 + ... + 20898.

It is an arithmetic number, because the mean of its divisors is an integer number (3546120).

Almost surely, 2^21153921 is an apocalyptic number.

It is an amenable number.

21153921 is a deficient number, since it is larger than the sum of its proper divisors (7215039).

21153921 is a wasteful number, since it uses less digits than its factorization.

21153921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40935.

The product of its digits is 540, while the sum is 24.

The square root of 21153921 is about 4599.3391916666. The cubic root of 21153921 is about 276.5648351873.

The spelling of 21153921 in words is "twenty-one million, one hundred fifty-three thousand, nine hundred twenty-one".