640261 has 2 divisors, whose sum is σ = 640262. Its totient is φ = 640260.

The previous prime is 640259. The next prime is 640267. The reversal of 640261 is 162046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 504100 + 136161 = 710^2 + 369^2 .

It is a cyclic number.

It is not a de Polignac number, because 640261 - 2¹ = 640259 is a prime.

Together with 640259, it forms a pair of twin primes.

640261 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640267) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320130 + 320131.

It is an arithmetic number, because the mean of its divisors is an integer number (320131).

2⁶⁴⁰²⁶¹ is an apocalyptic number.

It is an amenable number.

640261 is a deficient number, since it is larger than the sum of its proper divisors (1).

640261 is an equidigital number, since it uses as much as digits as its factorization.

640261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 640261 is about 800.1631083723. The cubic root of 640261 is about 86.1891007478.

The spelling of 640261 in words is "six hundred forty thousand, two hundred sixty-one".