21661311167 has 4 divisors (see below), whose sum is σ = 22122190176. Its totient is φ = 21200432160.

The previous prime is 21661311157. The next prime is 21661311187. The reversal of 21661311167 is 76111316612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21661311167 - 2¹⁸ = 21661049023 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 (21661311137) 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, 230439434 + ... + 230439527.

It is an arithmetic number, because the mean of its divisors is an integer number (5530547544).

Almost surely, 2^21661311167 is an apocalyptic number.

21661311167 is a deficient number, since it is larger than the sum of its proper divisors (460879009).

21661311167 is an equidigital number, since it uses as much as digits as its factorization.

21661311167 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 460879008.

The product of its digits is 9072, while the sum is 35.

Adding to 21661311167 its reverse (76111316612), we get a palindrome (97772627779).

Subtracting 21661311167 from its reverse (76111316612), we obtain a palindrome (54450005445).

The spelling of 21661311167 in words is "twenty-one billion, six hundred sixty-one million, three hundred eleven thousand, one hundred sixty-seven".