16721618 has 4 divisors (see below), whose sum is σ = 25082430. Its totient is φ = 8360808.

The previous prime is 16721611. The next prime is 16721629. The reversal of 16721618 is 81612761.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 81612761 = 641 ⋅127321.

It can be written as a sum of positive squares in only one way, i.e., 16345849 + 375769 = 4043^2 + 613^2 .

It is a super-2 number, since 2×16721618² = 559225017075848, which contains 22 as substring.

It is an alternating number because its digits alternate between odd and even.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (16721611) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4180403 + ... + 4180406.

Almost surely, 2^16721618 is an apocalyptic number.

16721618 is a deficient number, since it is larger than the sum of its proper divisors (8360812).

16721618 is an equidigital number, since it uses as much as digits as its factorization.

16721618 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8360811.

The product of its digits is 4032, while the sum is 32.

The square root of 16721618 is about 4089.2075026831. The cubic root of 16721618 is about 255.7169009974.

The spelling of 16721618 in words is "sixteen million, seven hundred twenty-one thousand, six hundred eighteen".