640729261 has 4 divisors (see below), whose sum is σ = 640797052. Its totient is φ = 640661472.

The previous prime is 640729231. The next prime is 640729307. The reversal of 640729261 is 162927046.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 385336900 + 255392361 = 19630^2 + 15981^2 .

It is a cyclic number.

It is not a de Polignac number, because 640729261 - 2¹³ = 640721069 is a prime.

It is a super-2 number, since 2×640729261² = 821067971803212242, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 640729261.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640729211) 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, 16866 + ... + 39571.

It is an arithmetic number, because the mean of its divisors is an integer number (160199263).

Almost surely, 2^640729261 is an apocalyptic number.

It is an amenable number.

640729261 is a deficient number, since it is larger than the sum of its proper divisors (67791).

640729261 is a wasteful number, since it uses less digits than its factorization.

640729261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 67790.

The product of its (nonzero) digits is 36288, while the sum is 37.

The square root of 640729261 is about 25312.6304638613. The cubic root of 640729261 is about 862.1010736828.

The spelling of 640729261 in words is "six hundred forty million, seven hundred twenty-nine thousand, two hundred sixty-one".