3645721 has 4 divisors (see below), whose sum is σ = 3744292. Its totient is φ = 3547152.

The previous prime is 3645713. The next prime is 3645727. The reversal of 3645721 is 1275463.

3645721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is the 780-th star number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1275463 = 7 ⋅182209.

It can be written as a sum of positive squares in 2 ways, for example, as 3013696 + 632025 = 1736^2 + 795^2 .

It is a cyclic number.

It is not a de Polignac number, because 3645721 - 2³ = 3645713 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 3645721.

It is not an unprimeable number, because it can be changed into a prime (3645727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 49230 + ... + 49303.

It is an arithmetic number, because the mean of its divisors is an integer number (936073).

Almost surely, 2^3645721 is an apocalyptic number.

It is an amenable number.

3645721 is a deficient number, since it is larger than the sum of its proper divisors (98571).

3645721 is an equidigital number, since it uses as much as digits as its factorization.

3645721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 98570.

The product of its digits is 5040, while the sum is 28.

The square root of 3645721 is about 1909.3771235667. The cubic root of 3645721 is about 153.9079817966.

The spelling of 3645721 in words is "three million, six hundred forty-five thousand, seven hundred twenty-one".