3661721 has 6 divisors (see below), whose sum is σ = 4259610. Its totient is φ = 3138576.

The previous prime is 3661703. The next prime is 3661733. The reversal of 3661721 is 1271663.

3661721 = 249² + 250² + ... + 297².

It can be written as a sum of positive squares in only one way, i.e., 3013696 + 648025 = 1736^2 + 805^2 .

It is not a de Polignac number, because 3661721 - 2¹⁸ = 3399577 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (3661771) 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, 37316 + ... + 37413.

It is an arithmetic number, because the mean of its divisors is an integer number (709935).

Almost surely, 2^3661721 is an apocalyptic number.

It is an amenable number.

3661721 is a deficient number, since it is larger than the sum of its proper divisors (597889).

3661721 is an equidigital number, since it uses as much as digits as its factorization.

3661721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 74743 (or 74736 counting only the distinct ones).

The product of its digits is 1512, while the sum is 26.

The square root of 3661721 is about 1913.5623846637. The cubic root of 3661721 is about 154.1328055493.

The spelling of 3661721 in words is "three million, six hundred sixty-one thousand, seven hundred twenty-one".