1646556721 has 4 divisors (see below), whose sum is σ = 1691058292. Its totient is φ = 1602055152.

The previous prime is 1646556689. The next prime is 1646556773. The reversal of 1646556721 is 1276556461.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1033301025 + 613255696 = 32145^2 + 24764^2 .

It is a cyclic number.

It is not a de Polignac number, because 1646556721 - 2⁵ = 1646556689 is a prime.

It is a super-2 number, since 2×1646556721² = 5422298070940543682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1646556221) 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, 22250730 + ... + 22250803.

It is an arithmetic number, because the mean of its divisors is an integer number (422764573).

Almost surely, 2^1646556721 is an apocalyptic number.

It is an amenable number.

1646556721 is a deficient number, since it is larger than the sum of its proper divisors (44501571).

1646556721 is an equidigital number, since it uses as much as digits as its factorization.

1646556721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44501570.

The product of its digits is 302400, while the sum is 43.

The square root of 1646556721 is about 40577.7860534554. The cubic root of 1646556721 is about 1180.8431972435.

The spelling of 1646556721 in words is "one billion, six hundred forty-six million, five hundred fifty-six thousand, seven hundred twenty-one".