21366736681 has 4 divisors (see below), whose sum is σ = 21369779200. Its totient is φ = 21363694164.

The previous prime is 21366736649. The next prime is 21366736687. The reversal of 21366736681 is 18663766312.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21366736681 - 2⁵ = 21366736649 is a prime.

It is a super-2 number, since 2×21366736681² (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 (21366736687) 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, 1510701 + ... + 1524778.

It is an arithmetic number, because the mean of its divisors is an integer number (5342444800).

Almost surely, 2^21366736681 is an apocalyptic number.

It is an amenable number.

21366736681 is a deficient number, since it is larger than the sum of its proper divisors (3042519).

21366736681 is an equidigital number, since it uses as much as digits as its factorization.

21366736681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3042518.

The product of its digits is 1306368, while the sum is 49.

The spelling of 21366736681 in words is "twenty-one billion, three hundred sixty-six million, seven hundred thirty-six thousand, six hundred eighty-one".