21451643 has 4 divisors (see below), whose sum is σ = 21615528. Its totient is φ = 21287760.

The previous prime is 21451631. The next prime is 21451649. The reversal of 21451643 is 34615412.

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 21451643 - 2⁶ = 21451579 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21451649) 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, 81746 + ... + 82007.

It is an arithmetic number, because the mean of its divisors is an integer number (5403882).

Almost surely, 2^21451643 is an apocalyptic number.

21451643 is a deficient number, since it is larger than the sum of its proper divisors (163885).

21451643 is a wasteful number, since it uses less digits than its factorization.

21451643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 163884.

The product of its digits is 2880, while the sum is 26.

The square root of 21451643 is about 4631.5918429844. The cubic root of 21451643 is about 277.8562607686.

The spelling of 21451643 in words is "twenty-one million, four hundred fifty-one thousand, six hundred forty-three".