16643891 has 16 divisors (see below), whose sum is σ = 18683136. Its totient is φ = 14700000.

The previous prime is 16643863. The next prime is 16643897. The reversal of 16643891 is 19834661.

It is a cyclic number.

It is not a de Polignac number, because 16643891 - 2¹⁸ = 16381747 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16643897) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 78776 + ... + 78986.

It is an arithmetic number, because the mean of its divisors is an integer number (1167696).

Almost surely, 2^16643891 is an apocalyptic number.

16643891 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

16643891 is a deficient number, since it is larger than the sum of its proper divisors (2039245).

16643891 is a wasteful number, since it uses less digits than its factorization.

16643891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 394.

The product of its digits is 31104, while the sum is 38.

The square root of 16643891 is about 4079.6925129230. The cubic root of 16643891 is about 255.3200697018.

It can be divided in two parts, 1664 and 3891, that added together give a palindrome (5555).

The spelling of 16643891 in words is "sixteen million, six hundred forty-three thousand, eight hundred ninety-one".