1721985891 has 16 divisors (see below), whose sum is σ = 2317374624. Its totient is φ = 1137337344.

The previous prime is 1721985871. The next prime is 1721985929. The reversal of 1721985891 is 1985891271.

It is not a de Polignac number, because 1721985891 - 2⁷ = 1721985763 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1721985821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 161085 + ... + 171441.

It is an arithmetic number, because the mean of its divisors is an integer number (144835914).

Almost surely, 2^1721985891 is an apocalyptic number.

1721985891 is a deficient number, since it is larger than the sum of its proper divisors (595388733).

1721985891 is a wasteful number, since it uses less digits than its factorization.

1721985891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10870.

The product of its digits is 362880, while the sum is 51.

The square root of 1721985891 is about 41496.8178418538. The cubic root of 1721985891 is about 1198.6062269295.

The spelling of 1721985891 in words is "one billion, seven hundred twenty-one million, nine hundred eighty-five thousand, eight hundred ninety-one".