21643151 has 4 divisors (see below), whose sum is σ = 21707712. Its totient is φ = 21578592.

The previous prime is 21643129. The next prime is 21643183. The reversal of 21643151 is 15134612.

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 21643151 - 2⁶ = 21643087 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 (21643051) 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, 31775 + ... + 32448.

It is an arithmetic number, because the mean of its divisors is an integer number (5426928).

Almost surely, 2^21643151 is an apocalyptic number.

21643151 is a deficient number, since it is larger than the sum of its proper divisors (64561).

21643151 is an equidigital number, since it uses as much as digits as its factorization.

21643151 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 64560.

The product of its digits is 720, while the sum is 23.

The square root of 21643151 is about 4652.2200076953. The cubic root of 21643151 is about 278.6806596213.

Adding to 21643151 its reverse (15134612), we get a palindrome (36777763).

The spelling of 21643151 in words is "twenty-one million, six hundred forty-three thousand, one hundred fifty-one".