21640165201 has 4 divisors (see below), whose sum is σ = 21644053812. Its totient is φ = 21636276592.

The previous prime is 21640165177. The next prime is 21640165207. The reversal of 21640165201 is 10256104612.

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 6814667601 + 14825497600 = 82551^2 + 121760^2 .

It is a cyclic number.

It is not a de Polignac number, because 21640165201 - 2¹³ = 21640157009 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21640165201.

It is not an unprimeable number, because it can be changed into a prime (21640165207) 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, 1935946 + ... + 1947091.

It is an arithmetic number, because the mean of its divisors is an integer number (5411013453).

Almost surely, 2^21640165201 is an apocalyptic number.

It is an amenable number.

21640165201 is a deficient number, since it is larger than the sum of its proper divisors (3888611).

21640165201 is an equidigital number, since it uses as much as digits as its factorization.

21640165201 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3888610.

The product of its (nonzero) digits is 2880, while the sum is 28.

Adding to 21640165201 its reverse (10256104612), we get a palindrome (31896269813).

The spelling of 21640165201 in words is "twenty-one billion, six hundred forty million, one hundred sixty-five thousand, two hundred one".