64777991 has 4 divisors (see below), whose sum is σ = 66357984. Its totient is φ = 63198000.

The previous prime is 64777987. The next prime is 64777997. The reversal of 64777991 is 19977746.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19977746 = 2 ⋅9988873.

It is a cyclic number.

It is not a de Polignac number, because 64777991 - 2² = 64777987 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (64777997) 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, 789935 + ... + 790016.

It is an arithmetic number, because the mean of its divisors is an integer number (16589496).

Almost surely, 2^64777991 is an apocalyptic number.

64777991 is a deficient number, since it is larger than the sum of its proper divisors (1579993).

64777991 is a wasteful number, since it uses less digits than its factorization.

64777991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1579992.

The product of its digits is 666792, while the sum is 50.

The square root of 64777991 is about 8048.4775578988. The cubic root of 64777991 is about 401.6142909809.

The spelling of 64777991 in words is "sixty-four million, seven hundred seventy-seven thousand, nine hundred ninety-one".