645948661 has 4 divisors (see below), whose sum is σ = 646039692. Its totient is φ = 645857632.

The previous prime is 645948613. The next prime is 645948673. The reversal of 645948661 is 166849546.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 441630225 + 204318436 = 21015^2 + 14294^2 .

It is a cyclic number.

It is not a de Polignac number, because 645948661 - 2⁷ = 645948533 is a prime.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645948691) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 33880 + ... + 49393.

It is an arithmetic number, because the mean of its divisors is an integer number (161509923).

Almost surely, 2^645948661 is an apocalyptic number.

It is an amenable number.

645948661 is a deficient number, since it is larger than the sum of its proper divisors (91031).

645948661 is an equidigital number, since it uses as much as digits as its factorization.

645948661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91030.

The product of its digits is 1244160, while the sum is 49.

The square root of 645948661 is about 25415.5200812417. The cubic root of 645948661 is about 864.4356464456.

The spelling of 645948661 in words is "six hundred forty-five million, nine hundred forty-eight thousand, six hundred sixty-one".