16643521 has 2 divisors, whose sum is σ = 16643522. Its totient is φ = 16643520.

The previous prime is 16643519. The next prime is 16643531. The reversal of 16643521 is 12534661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13542400 + 3101121 = 3680^2 + 1761^2 .

It is a cyclic number.

It is not a de Polignac number, because 16643521 - 2¹ = 16643519 is a prime.

Together with 16643519, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 16643521.

It is not a weakly prime, because it can be changed into another prime (16643531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8321760 + 8321761.

It is an arithmetic number, because the mean of its divisors is an integer number (8321761).

Almost surely, 2^16643521 is an apocalyptic number.

It is an amenable number.

16643521 is a deficient number, since it is larger than the sum of its proper divisors (1).

16643521 is an equidigital number, since it uses as much as digits as its factorization.

16643521 is an evil number, because the sum of its binary digits is even.

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

The square root of 16643521 is about 4079.6471661162. The cubic root of 16643521 is about 255.3181777338.

The spelling of 16643521 in words is "sixteen million, six hundred forty-three thousand, five hundred twenty-one".