64640491 has 4 divisors (see below), whose sum is σ = 64918152. Its totient is φ = 64362832.

The previous prime is 64640473. The next prime is 64640497. The reversal of 64640491 is 19404646.

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

It is a cyclic number.

It is not a de Polignac number, because 64640491 - 2²³ = 56251883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (64640497) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 138481 + ... + 138946.

It is an arithmetic number, because the mean of its divisors is an integer number (16229538).

Almost surely, 2^64640491 is an apocalyptic number.

64640491 is a deficient number, since it is larger than the sum of its proper divisors (277661).

64640491 is a wasteful number, since it uses less digits than its factorization.

64640491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 277660.

The product of its (nonzero) digits is 20736, while the sum is 34.

The square root of 64640491 is about 8039.9310320425. The cubic root of 64640491 is about 401.3299295678.

The spelling of 64640491 in words is "sixty-four million, six hundred forty thousand, four hundred ninety-one".