640653721 has 8 divisors (see below), whose sum is σ = 680512104. Its totient is φ = 601036800.

The previous prime is 640653697. The next prime is 640653731. The reversal of 640653721 is 127356046.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 9388096 + 631265625 = 3064^2 + 25125^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 640653721 - 2⁷ = 640653593 is a prime.

It is a super-2 number, since 2×640653721² = 820874380462291682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640653731) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 54880 + ... + 65521.

It is an arithmetic number, because the mean of its divisors is an integer number (85064013).

Almost surely, 2^640653721 is an apocalyptic number.

It is an amenable number.

640653721 is a deficient number, since it is larger than the sum of its proper divisors (39858383).

640653721 is a wasteful number, since it uses less digits than its factorization.

640653721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 120731.

The product of its (nonzero) digits is 30240, while the sum is 34.

The square root of 640653721 is about 25311.1382794216. The cubic root of 640653721 is about 862.0671926670.

The spelling of 640653721 in words is "six hundred forty million, six hundred fifty-three thousand, seven hundred twenty-one".