640644621565 has 16 divisors (see below), whose sum is σ = 827974745136. Its totient is φ = 473054400000.

The previous prime is 640644621559. The next prime is 640644621569. The reversal of 640644621565 is 565126446046.

640644621565 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 8 ways, for example, as 437263465081 + 203381156484 = 661259^2 + 450978^2 .

It is not a de Polignac number, because 640644621565 - 2²¹ = 640642524413 is a prime.

It is a super-2 number, since 2×640644621565² (a number of 24 digits) 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 (640644621569) 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, 466015 + ... + 1224115.

It is an arithmetic number, because the mean of its divisors is an integer number (51748421571).

Almost surely, 2^640644621565 is an apocalyptic number.

640644621565 is a gapful number since it is divisible by the number (65) formed by its first and last digit.

It is an amenable number.

640644621565 is a deficient number, since it is larger than the sum of its proper divisors (187330123571).

640644621565 is a wasteful number, since it uses less digits than its factorization.

640644621565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 771120.

The product of its (nonzero) digits is 4147200, while the sum is 49.

The spelling of 640644621565 in words is "six hundred forty billion, six hundred forty-four million, six hundred twenty-one thousand, five hundred sixty-five".