21768346681 has 3 divisors (see below), whose sum is σ = 21768494223. Its totient is φ = 21768199140.

The previous prime is 21768346679. The next prime is 21768346693. The reversal of 21768346681 is 18664386712.

The square root of 21768346681 is 147541.

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., 702727081 + 21065619600 = 26509^2 + 145140^2 .

It is not a de Polignac number, because 21768346681 - 2¹ = 21768346679 is a prime.

It is a super-2 number, since 2×21768346681² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21768346651) 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, 73771 + ... + 221311.

It is an arithmetic number, because the mean of its divisors is an integer number (7256164741).

Almost surely, 2^21768346681 is an apocalyptic number.

21768346681 is the 147541-st square number.

21768346681 is the 73771-st centered octagonal number.

It is an amenable number.

21768346681 is a deficient number, since it is larger than the sum of its proper divisors (147542).

21768346681 is an frugal number, since it uses more digits than its factorization.

21768346681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 295082 (or 147541 counting only the distinct ones).

The product of its digits is 2322432, while the sum is 52.

It can be divided in two parts, 21768 and 346681, that added together give a square (368449 = 607²).

The spelling of 21768346681 in words is "twenty-one billion, seven hundred sixty-eight million, three hundred forty-six thousand, six hundred eighty-one".