640051721 has 16 divisors (see below), whose sum is σ = 670507200. Its totient is φ = 610209600.

The previous prime is 640051693. The next prime is 640051729. The reversal of 640051721 is 127150046.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640051721 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (640051729) 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, 1257215 + ... + 1257723.

It is an arithmetic number, because the mean of its divisors is an integer number (41906700).

Almost surely, 2^640051721 is an apocalyptic number.

It is an amenable number.

640051721 is a deficient number, since it is larger than the sum of its proper divisors (30455479).

640051721 is a wasteful number, since it uses less digits than its factorization.

640051721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1000.

The product of its (nonzero) digits is 1680, while the sum is 26.

The square root of 640051721 is about 25299.2434867132. The cubic root of 640051721 is about 861.7970898701.

The spelling of 640051721 in words is "six hundred forty million, fifty-one thousand, seven hundred twenty-one".