640020581 has 2 divisors, whose sum is σ = 640020582. Its totient is φ = 640020580.

The previous prime is 640020569. The next prime is 640020599. The reversal of 640020581 is 185020046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 344696356 + 295324225 = 18566^2 + 17185^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640020581 is a prime.

It is a super-2 number, since 2×640020581² = 819252688207155122, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 640020581.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640020551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320010290 + 320010291.

It is an arithmetic number, because the mean of its divisors is an integer number (320010291).

Almost surely, 2^640020581 is an apocalyptic number.

It is an amenable number.

640020581 is a deficient number, since it is larger than the sum of its proper divisors (1).

640020581 is an equidigital number, since it uses as much as digits as its factorization.

640020581 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1920, while the sum is 26.

The square root of 640020581 is about 25298.6280458052. The cubic root of 640020581 is about 861.7831135013.

The spelling of 640020581 in words is "six hundred forty million, twenty thousand, five hundred eighty-one".