1720661 has 4 divisors (see below), whose sum is σ = 1723692. Its totient is φ = 1717632.

The previous prime is 1720643. The next prime is 1720669. The reversal of 1720661 is 1660271.

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 1322500 + 398161 = 1150^2 + 631^2 .

It is a cyclic number.

It is not a de Polignac number, because 1720661 - 2⁶ = 1720597 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1720669) 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, 380 + ... + 1893.

It is an arithmetic number, because the mean of its divisors is an integer number (430923).

2^1720661 is an apocalyptic number.

It is an amenable number.

1720661 is a deficient number, since it is larger than the sum of its proper divisors (3031).

1720661 is an equidigital number, since it uses as much as digits as its factorization.

1720661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3030.

The product of its (nonzero) digits is 504, while the sum is 23.

The square root of 1720661 is about 1311.7396845411. The cubic root of 1720661 is about 119.8298746661.

The spelling of 1720661 in words is "one million, seven hundred twenty thousand, six hundred sixty-one".