21161231165 has 32 divisors (see below), whose sum is σ = 26529085440. Its totient is φ = 16190669376.

The previous prime is 21161231137. The next prime is 21161231173. The reversal of 21161231165 is 56113216112.

It is a cyclic number.

It is not a de Polignac number, because 21161231165 - 2¹⁸ = 21160969021 is a prime.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 3332984 + ... + 3339326.

It is an arithmetic number, because the mean of its divisors is an integer number (829033920).

Almost surely, 2^21161231165 is an apocalyptic number.

It is an amenable number.

21161231165 is a deficient number, since it is larger than the sum of its proper divisors (5367854275).

21161231165 is a wasteful number, since it uses less digits than its factorization.

21161231165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6713.

The product of its digits is 2160, while the sum is 29.

Adding to 21161231165 its reverse (56113216112), we get a palindrome (77274447277).

The spelling of 21161231165 in words is "twenty-one billion, one hundred sixty-one million, two hundred thirty-one thousand, one hundred sixty-five".