640661506 has 4 divisors (see below), whose sum is σ = 960992262. Its totient is φ = 320330752.

The previous prime is 640661501. The next prime is 640661519. The reversal of 640661506 is 605166046.

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

It can be written as a sum of positive squares in only one way, i.e., 428697025 + 211964481 = 20705^2 + 14559^2 .

It is not an unprimeable number, because it can be changed into a prime (640661501) 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 as a sum of consecutive naturals, namely, 160165375 + ... + 160165378.

Almost surely, 2^640661506 is an apocalyptic number.

640661506 is a deficient number, since it is larger than the sum of its proper divisors (320330756).

640661506 is a wasteful number, since it uses less digits than its factorization.

640661506 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 320330755.

The product of its (nonzero) digits is 25920, while the sum is 34.

The square root of 640661506 is about 25311.2920650053. The cubic root of 640661506 is about 862.0706844993.

The spelling of 640661506 in words is "six hundred forty million, six hundred sixty-one thousand, five hundred six".