1721661 has 4 divisors (see below), whose sum is σ = 2295552. Its totient is φ = 1147772.

The previous prime is 1721659. The next prime is 1721683. The reversal of 1721661 is 1661271.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1661271 = 3 ⋅553757.

It is a cyclic number.

It is not a de Polignac number, because 1721661 - 2¹ = 1721659 is a prime.

It is a D-number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1721651) 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, 286941 + ... + 286946.

It is an arithmetic number, because the mean of its divisors is an integer number (573888).

2^1721661 is an apocalyptic number.

It is an amenable number.

1721661 is a deficient number, since it is larger than the sum of its proper divisors (573891).

1721661 is an equidigital number, since it uses as much as digits as its factorization.

1721661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 573890.

The product of its digits is 504, while the sum is 24.

The square root of 1721661 is about 1312.1208023654. The cubic root of 1721661 is about 119.8530840933.

The spelling of 1721661 in words is "one million, seven hundred twenty-one thousand, six hundred sixty-one".