640209616661 has 2 divisors, whose sum is σ = 640209616662. Its totient is φ = 640209616660.

The previous prime is 640209616649. The next prime is 640209616679. The reversal of 640209616661 is 166616902046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 608136388561 + 32073228100 = 779831^2 + 179090^2 .

It is a cyclic number.

It is not a de Polignac number, because 640209616661 - 2⁶ = 640209616597 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640209616561) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320104808330 + 320104808331.

It is an arithmetic number, because the mean of its divisors is an integer number (320104808331).

Almost surely, 2^640209616661 is an apocalyptic number.

It is an amenable number.

640209616661 is a deficient number, since it is larger than the sum of its proper divisors (1).

640209616661 is an equidigital number, since it uses as much as digits as its factorization.

640209616661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 559872, while the sum is 47.

The spelling of 640209616661 in words is "six hundred forty billion, two hundred nine million, six hundred sixteen thousand, six hundred sixty-one".