1640721 has 16 divisors (see below), whose sum is σ = 2363904. Its totient is φ = 1008384.

The previous prime is 1640701. The next prime is 1640729. The reversal of 1640721 is 1270461.

It is not a de Polignac number, because 1640721 - 2⁵ = 1640689 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1640729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2400 + ... + 3006.

It is an arithmetic number, because the mean of its divisors is an integer number (147744).

2^1640721 is an apocalyptic number.

It is an amenable number.

1640721 is a deficient number, since it is larger than the sum of its proper divisors (723183).

1640721 is a wasteful number, since it uses less digits than its factorization.

1640721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 680.

The product of its (nonzero) digits is 336, while the sum is 21.

The square root of 1640721 is about 1280.9063197596. The cubic root of 1640721 is about 117.9446499005.

The spelling of 1640721 in words is "one million, six hundred forty thousand, seven hundred twenty-one".