1664721 has 6 divisors (see below), whose sum is σ = 2404610. Its totient is φ = 1109808.

The previous prime is 1664713. The next prime is 1664771. The reversal of 1664721 is 1274661.

1664721 is a `hidden beast` number, since 16 + 647 + 2 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 1535121 + 129600 = 1239^2 + 360^2 .

It is not a de Polignac number, because 1664721 - 2³ = 1664713 is a prime.

It is a Duffinian number.

1664721 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (1664701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 92476 + ... + 92493.

2^1664721 is an apocalyptic number.

It is an amenable number.

1664721 is a deficient number, since it is larger than the sum of its proper divisors (739889).

1664721 is a wasteful number, since it uses less digits than its factorization.

1664721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 184975 (or 184972 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 1664721 is about 1290.2406752230. The cubic root of 1664721 is about 118.5169553264.

The spelling of 1664721 in words is "one million, six hundred sixty-four thousand, seven hundred twenty-one".