640510621 has 4 divisors (see below), whose sum is σ = 644809500. Its totient is φ = 636211744.

The previous prime is 640510609. The next prime is 640510639. The reversal of 640510621 is 126015046.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 126015046 = 2 ⋅63007523.

It can be written as a sum of positive squares in 2 ways, for example, as 93605625 + 546904996 = 9675^2 + 23386^2 .

It is a cyclic number.

It is not a de Polignac number, because 640510621 - 2²³ = 632122013 is a prime.

It is a super-2 number, since 2×640510621² = 820507711227611282, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640510681) 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, 2149216 + ... + 2149513.

It is an arithmetic number, because the mean of its divisors is an integer number (161202375).

Almost surely, 2^640510621 is an apocalyptic number.

It is an amenable number.

640510621 is a deficient number, since it is larger than the sum of its proper divisors (4298879).

640510621 is a wasteful number, since it uses less digits than its factorization.

640510621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4298878.

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 640510621 is about 25308.3113028112. The cubic root of 640510621 is about 862.0030025035.

Adding to 640510621 its reverse (126015046), we get a palindrome (766525667).

The spelling of 640510621 in words is "six hundred forty million, five hundred ten thousand, six hundred twenty-one".