16643581 has 6 divisors (see below), whose sum is σ = 17061146. Its totient is φ = 16236000.

The previous prime is 16643579. The next prime is 16643603. The reversal of 16643581 is 18534661.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 241081 + 16402500 = 491^2 + 4050^2 .

It is not a de Polignac number, because 16643581 - 2¹ = 16643579 is a prime.

It is a super-2 number, since 2×16643581² = 554017577007122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16643521) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 3270 + ... + 6631.

Almost surely, 2^16643581 is an apocalyptic number.

It is an amenable number.

16643581 is a deficient number, since it is larger than the sum of its proper divisors (417565).

16643581 is an frugal number, since it uses more digits than its factorization.

16643581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9983 (or 9942 counting only the distinct ones).

The product of its digits is 17280, while the sum is 34.

The square root of 16643581 is about 4079.6545196867. The cubic root of 16643581 is about 255.3184845414.

The spelling of 16643581 in words is "sixteen million, six hundred forty-three thousand, five hundred eighty-one".