1671720721 has 16 divisors (see below), whose sum is σ = 1933744320. Its totient is φ = 1428295680.

The previous prime is 1671720709. The next prime is 1671720727. The reversal of 1671720721 is 1270271761.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1671720721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1671720727) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 132145 + ... + 144241.

It is an arithmetic number, because the mean of its divisors is an integer number (120859020).

Almost surely, 2^1671720721 is an apocalyptic number.

1671720721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1671720721 is a deficient number, since it is larger than the sum of its proper divisors (262023599).

1671720721 is a wasteful number, since it uses less digits than its factorization.

1671720721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12864.

The product of its (nonzero) digits is 8232, while the sum is 34.

The square root of 1671720721 is about 40886.6814623051. The cubic root of 1671720721 is about 1186.8283409296.

The spelling of 1671720721 in words is "one billion, six hundred seventy-one million, seven hundred twenty thousand, seven hundred twenty-one".