640981969 has 4 divisors (see below), whose sum is σ = 658305844. Its totient is φ = 623658096.

The previous prime is 640981949. The next prime is 640981981. The reversal of 640981969 is 969189046.

640981969 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 608263569 + 32718400 = 24663^2 + 5720^2 .

It is a cyclic number.

It is not a de Polignac number, because 640981969 - 2¹³ = 640973777 is a prime.

It is a super-2 number, since 2×640981969² = 821715769166233922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640981909) 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, 8661882 + ... + 8661955.

It is an arithmetic number, because the mean of its divisors is an integer number (164576461).

Almost surely, 2^640981969 is an apocalyptic number.

It is an amenable number.

640981969 is a deficient number, since it is larger than the sum of its proper divisors (17323875).

640981969 is a wasteful number, since it uses less digits than its factorization.

640981969 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17323874.

The product of its (nonzero) digits is 839808, while the sum is 52.

The square root of 640981969 is about 25317.6217089994. The cubic root of 640981969 is about 862.2143983041.

The spelling of 640981969 in words is "six hundred forty million, nine hundred eighty-one thousand, nine hundred sixty-nine".