65645721 has 28 divisors (see below), whose sum is σ = 104232852. Its totient is φ = 41181696.

The previous prime is 65645689. The next prime is 65645731. The reversal of 65645721 is 12754656.

It is a happy number.

65645721 is a `hidden beast` number, since 6 + 5 + 645 + 7 + 2 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 52359696 + 13286025 = 7236^2 + 3645^2 .

It is not a de Polignac number, because 65645721 - 2⁵ = 65645689 is a prime.

It is not an unprimeable number, because it can be changed into a prime (65645731) by changing a digit.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 9745 + ... + 15041.

Almost surely, 2^65645721 is an apocalyptic number.

It is an amenable number.

65645721 is a deficient number, since it is larger than the sum of its proper divisors (38587131).

65645721 is an equidigital number, since it uses as much as digits as its factorization.

65645721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5332 (or 5317 counting only the distinct ones).

The product of its digits is 50400, while the sum is 36.

The square root of 65645721 is about 8102.2046999567. The cubic root of 65645721 is about 403.3996101879.

It can be divided in two parts, 65645 and 721, that added together give a palindrome (66366).

The spelling of 65645721 in words is "sixty-five million, six hundred forty-five thousand, seven hundred twenty-one".