64400721 has 32 divisors (see below), whose sum is σ = 108441600. Its totient is φ = 33022080.

The previous prime is 64400717. The next prime is 64400723. The reversal of 64400721 is 12700446.

It is not a de Polignac number, because 64400721 - 2² = 64400717 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 64400691 and 64400700.

It is not an unprimeable number, because it can be changed into a prime (64400723) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 16485 + ... + 20013.

It is an arithmetic number, because the mean of its divisors is an integer number (3388800).

Almost surely, 2^64400721 is an apocalyptic number.

It is an amenable number.

64400721 is a deficient number, since it is larger than the sum of its proper divisors (44040879).

64400721 is a wasteful number, since it uses less digits than its factorization.

64400721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3629.

The product of its (nonzero) digits is 1344, while the sum is 24.

The square root of 64400721 is about 8025.0059813062. The cubic root of 64400721 is about 400.8330990769.

The spelling of 64400721 in words is "sixty-four million, four hundred thousand, seven hundred twenty-one".