1720721 has 4 divisors (see below), whose sum is σ = 1723392. Its totient is φ = 1718052.

The previous prime is 1720711. The next prime is 1720769. The reversal of 1720721 is 1270271.

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 a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1720721 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 1720693 and 1720702.

It is not an unprimeable number, because it can be changed into a prime (1720711) 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, 296 + ... + 1878.

It is an arithmetic number, because the mean of its divisors is an integer number (430848).

2^1720721 is an apocalyptic number.

It is an amenable number.

1720721 is a deficient number, since it is larger than the sum of its proper divisors (2671).

1720721 is a wasteful number, since it uses less digits than its factorization.

1720721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2670.

The product of its (nonzero) digits is 196, while the sum is 20.

The square root of 1720721 is about 1311.7625547331. The cubic root of 1720721 is about 119.8312674853.

Adding to 1720721 its reverse (1270271), we get a palindrome (2990992).

The spelling of 1720721 in words is "one million, seven hundred twenty thousand, seven hundred twenty-one".