21766638313729 has 3 divisors (see below), whose sum is σ = 21766642979203. Its totient is φ = 21766633648256.

The previous prime is 21766638313727. The next prime is 21766638313801. The reversal of 21766638313729 is 92731383666712.

The square root of 21766638313729 is 4665473.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 18182250324225 + 3584387989504 = 4264065^2 + 1893248^2 .

It is not a de Polignac number, because 21766638313729 - 2¹ = 21766638313727 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21766638313727) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 2332737 + ... + 6998209.

Almost surely, 2^{21766638313729} is an apocalyptic number.

21766638313729 is the 4665473-rd square number.

21766638313729 is the 2332737-th centered octagonal number.

It is an amenable number.

21766638313729 is a deficient number, since it is larger than the sum of its proper divisors (4665474).

21766638313729 is an frugal number, since it uses more digits than its factorization.

21766638313729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9330946 (or 4665473 counting only the distinct ones).

The product of its digits is 82301184, while the sum is 64.

The spelling of 21766638313729 in words is "twenty-one trillion, seven hundred sixty-six billion, six hundred thirty-eight million, three hundred thirteen thousand, seven hundred twenty-nine".