64657681 has 27 divisors (see below), whose sum is σ = 77293083.
Its totient is φ = 54035520.
The previous prime is 64657667. The next prime is 64657711. The reversal of 64657681 is 18675646.
It is a happy number.
The square root of 64657681 is 8041.
It is a perfect power (a square), and thus also a powerful number.
64657681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.
It can be written as a sum of positive squares in only one way, i.e., 50339025 + 14318656 = 7095^2 + 3784^2
It is not a de Polignac number, because 64657681 - 27 = 64657553 is a prime.
It is a super-2 number, since 2×646576812 = 8361231424595522, which contains 22 as substring.
It is a Harshad number since it is a multiple of its sum of digits (43).
It is a Duffinian number.
It is not an unprimeable number, because it can be changed into a prime (64657631) 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 in 26 ways as a sum of consecutive naturals, for example, 1503646 + ... + 1503688.
Almost surely, 264657681 is an apocalyptic number.
64657681 is the 8041-st square number.
64657681 is the 4021-st centered octagonal number.
It is an amenable number.
64657681 is a deficient number, since it is larger than the sum of its proper divisors (12635402).
64657681 is a wasteful number, since it uses less digits than its factorization.
64657681 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 142 (or 71 counting only the distinct ones).
The product of its digits is 241920, while the sum is 43.
The cubic root of 64657681 is about 401.3655019566.
The spelling of 64657681 in words is "sixty-four million, six hundred fifty-seven thousand, six hundred eighty-one".