640201666521 has 4 divisors (see below), whose sum is σ = 853602222032. Its totient is φ = 426801111012.

The previous prime is 640201666487. The next prime is 640201666529. The reversal of 640201666521 is 125666102046.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 640201666521 - 2³¹ = 638054182873 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 640201666521.

It is not an unprimeable number, because it can be changed into a prime (640201666529) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106700277751 + ... + 106700277756.

It is an arithmetic number, because the mean of its divisors is an integer number (213400555508).

Almost surely, 2^640201666521 is an apocalyptic number.

It is an amenable number.

640201666521 is a deficient number, since it is larger than the sum of its proper divisors (213400555511).

640201666521 is a wasteful number, since it uses less digits than its factorization.

640201666521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213400555510.

The product of its (nonzero) digits is 103680, while the sum is 39.

Adding to 640201666521 its reverse (125666102046), we get a palindrome (765867768567).

The spelling of 640201666521 in words is "six hundred forty billion, two hundred one million, six hundred sixty-six thousand, five hundred twenty-one".