21516643 has 4 divisors (see below), whose sum is σ = 21661200. Its totient is φ = 21372088.

The previous prime is 21516629. The next prime is 21516653. The reversal of 21516643 is 34661512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21516643 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21516613) 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, 72055 + ... + 72352.

It is an arithmetic number, because the mean of its divisors is an integer number (5415300).

Almost surely, 2^21516643 is an apocalyptic number.

21516643 is a deficient number, since it is larger than the sum of its proper divisors (144557).

21516643 is a wasteful number, since it uses less digits than its factorization.

21516643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 144556.

The product of its digits is 4320, while the sum is 28.

The square root of 21516643 is about 4638.6035614180. The cubic root of 21516643 is about 278.1366191838.

The spelling of 21516643 in words is "twenty-one million, five hundred sixteen thousand, six hundred forty-three".