21985211167921 has 9 divisors (see below), whose sum is σ = 23203322431083. Its totient is φ = 20828010391560.

The previous prime is 21985211167897. The next prime is 21985211167961. The reversal of 21985211167921 is 12976111258912.

The square root of 21985211167921 is 4688839.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 11002747727521 + 10982463440400 = 3317039^2 + 3313980^2 .

It is not a de Polignac number, because 21985211167921 - 2³⁷ = 21847772214449 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21985211167961) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 88964551 + ... + 89211331.

It is an arithmetic number, because the mean of its divisors is an integer number (2578146936787).

Almost surely, 2^{21985211167921} is an apocalyptic number.

21985211167921 is the 4688839-th square number.

21985211167921 is the 2344420-th centered octagonal number.

It is an amenable number.

21985211167921 is a deficient number, since it is larger than the sum of its proper divisors (1218111263162).

21985211167921 is an frugal number, since it uses more digits than its factorization.

21985211167921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 493600 (or 246800 counting only the distinct ones).

The product of its digits is 1088640, while the sum is 55.

Subtracting from 21985211167921 its reverse (12976111258912), we obtain a palindrome (9009099909009).

The spelling of 21985211167921 in words is "twenty-one trillion, nine hundred eighty-five billion, two hundred eleven million, one hundred sixty-seven thousand, nine hundred twenty-one".