1720888721 has 4 divisors (see below), whose sum is σ = 1723913700. Its totient is φ = 1717863744.

The previous prime is 1720888703. The next prime is 1720888783. The reversal of 1720888721 is 1278880271.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1278880271 = 24517 ⋅52163.

It can be written as a sum of positive squares in 2 ways, for example, as 159769600 + 1561119121 = 12640^2 + 39511^2 .

It is a cyclic number.

It is not a de Polignac number, because 1720888721 - 2⁶ = 1720888657 is a prime.

It is a super-2 number, since 2×1720888721² = 5922915980130031682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1720888021) 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, 1511636 + ... + 1512773.

It is an arithmetic number, because the mean of its divisors is an integer number (430978425).

Almost surely, 2^1720888721 is an apocalyptic number.

It is an amenable number.

1720888721 is a deficient number, since it is larger than the sum of its proper divisors (3024979).

1720888721 is an equidigital number, since it uses as much as digits as its factorization.

1720888721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3024978.

The product of its (nonzero) digits is 100352, while the sum is 44.

The square root of 1720888721 is about 41483.5958060533. The cubic root of 1720888721 is about 1198.3516073066.

The spelling of 1720888721 in words is "one billion, seven hundred twenty million, eight hundred eighty-eight thousand, seven hundred twenty-one".