18721645 has 4 divisors (see below), whose sum is σ = 22465980. Its totient is φ = 14977312.

The previous prime is 18721643. The next prime is 18721649. The reversal of 18721645 is 54612781.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 5076009 + 13645636 = 2253^2 + 3694^2 .

It is a cyclic number.

It is not a de Polignac number, because 18721645 - 2¹ = 18721643 is a prime.

It is a super-3 number, since 3×18721645³ (a number of 23 digits) contains 333 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 18721645.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18721643) 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, 1872160 + ... + 1872169.

It is an arithmetic number, because the mean of its divisors is an integer number (5616495).

Almost surely, 2^18721645 is an apocalyptic number.

It is an amenable number.

18721645 is a deficient number, since it is larger than the sum of its proper divisors (3744335).

18721645 is an equidigital number, since it uses as much as digits as its factorization.

18721645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3744334.

The product of its digits is 13440, while the sum is 34.

The square root of 18721645 is about 4326.8516267605. The cubic root of 18721645 is about 265.5306561377.

The spelling of 18721645 in words is "eighteen million, seven hundred twenty-one thousand, six hundred forty-five".