64507721 has 4 divisors (see below), whose sum is σ = 64880772. Its totient is φ = 64134672.

The previous prime is 64507699. The next prime is 64507757. The reversal of 64507721 is 12770546.

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

It can be written as a sum of positive squares in 2 ways, for example, as 50965321 + 13542400 = 7139^2 + 3680^2 .

It is a cyclic number.

It is not a de Polignac number, because 64507721 - 2⁶ = 64507657 is a prime.

It is a super-2 number, since 2×64507721² = 8322492137227682, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (64507921) 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, 186266 + ... + 186611.

It is an arithmetic number, because the mean of its divisors is an integer number (16220193).

Almost surely, 2^64507721 is an apocalyptic number.

It is an amenable number.

64507721 is a deficient number, since it is larger than the sum of its proper divisors (373051).

64507721 is a wasteful number, since it uses less digits than its factorization.

64507721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 373050.

The product of its (nonzero) digits is 11760, while the sum is 32.

The square root of 64507721 is about 8031.6698761839. The cubic root of 64507721 is about 401.0549672475.

The spelling of 64507721 in words is "sixty-four million, five hundred seven thousand, seven hundred twenty-one".