16623521 has 4 divisors (see below), whose sum is σ = 16632000. Its totient is φ = 16615044.

The previous prime is 16623517. The next prime is 16623539. The reversal of 16623521 is 12532661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12532661 = 307 ⋅40823.

It is a cyclic number.

It is not a de Polignac number, because 16623521 - 2² = 16623517 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (16623511) 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, 380 + ... + 5778.

It is an arithmetic number, because the mean of its divisors is an integer number (4158000).

Almost surely, 2^16623521 is an apocalyptic number.

It is an amenable number.

16623521 is a deficient number, since it is larger than the sum of its proper divisors (8479).

16623521 is an equidigital number, since it uses as much as digits as its factorization.

16623521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8478.

The product of its digits is 2160, while the sum is 26.

The square root of 16623521 is about 4077.1952369245. The cubic root of 16623521 is about 255.2158674453.

The spelling of 16623521 in words is "sixteen million, six hundred twenty-three thousand, five hundred twenty-one".