1720021 has 4 divisors (see below), whose sum is σ = 1722700. Its totient is φ = 1717344.

The previous prime is 1720003. The next prime is 1720031. The reversal of 1720021 is 1200271.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1200271 = 421 ⋅2851.

It can be written as a sum of positive squares in 2 ways, for example, as 1347921 + 372100 = 1161^2 + 610^2 .

It is a cyclic number.

It is not a de Polignac number, because 1720021 - 2⁵ = 1719989 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1719983 and 1720010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1720031) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 265 + ... + 1873.

It is an arithmetic number, because the mean of its divisors is an integer number (430675).

2^1720021 is an apocalyptic number.

It is an amenable number.

1720021 is a deficient number, since it is larger than the sum of its proper divisors (2679).

1720021 is a wasteful number, since it uses less digits than its factorization.

1720021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2678.

The product of its (nonzero) digits is 28, while the sum is 13.

The square root of 1720021 is about 1311.4957110109. The cubic root of 1720021 is about 119.8150159132.

Adding to 1720021 its reverse (1200271), we get a palindrome (2920292).

The spelling of 1720021 in words is "one million, seven hundred twenty thousand, twenty-one".