65721442021 has 4 divisors (see below), whose sum is σ = 65814138700. Its totient is φ = 65628745344.

The previous prime is 65721442019. The next prime is 65721442091. The reversal of 65721442021 is 12024412756.

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 11764656225 + 53956785796 = 108465^2 + 232286^2 .

It is a cyclic number.

It is not a de Polignac number, because 65721442021 - 2¹ = 65721442019 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (65721442091) 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, 46347276 + ... + 46348693.

It is an arithmetic number, because the mean of its divisors is an integer number (16453534675).

Almost surely, 2^65721442021 is an apocalyptic number.

It is an amenable number.

65721442021 is a deficient number, since it is larger than the sum of its proper divisors (92696679).

65721442021 is an equidigital number, since it uses as much as digits as its factorization.

65721442021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 92696678.

The product of its (nonzero) digits is 26880, while the sum is 34.

Adding to 65721442021 its reverse (12024412756), we get a palindrome (77745854777).

The spelling of 65721442021 in words is "sixty-five billion, seven hundred twenty-one million, four hundred forty-two thousand, twenty-one".