64511991 has 16 divisors (see below), whose sum is σ = 101196000. Its totient is φ = 40477824.

The previous prime is 64511963. The next prime is 64512001. The reversal of 64511991 is 19911546.

64511991 is a `hidden beast` number, since 645 + 1 + 1 + 9 + 9 + 1 = 666.

It is not a de Polignac number, because 64511991 - 2⁶ = 64511927 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (64511191) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 69816 + ... + 70733.

It is an arithmetic number, because the mean of its divisors is an integer number (6324750).

Almost surely, 2^64511991 is an apocalyptic number.

64511991 is a deficient number, since it is larger than the sum of its proper divisors (36684009).

64511991 is a wasteful number, since it uses less digits than its factorization.

64511991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 140575 (or 140569 counting only the distinct ones).

The product of its digits is 9720, while the sum is 36.

The square root of 64511991 is about 8031.9356944637. The cubic root of 64511991 is about 401.0638161465.

The spelling of 64511991 in words is "sixty-four million, five hundred eleven thousand, nine hundred ninety-one".