21365516645731 has 4 divisors (see below), whose sum is σ = 21886626807864. Its totient is φ = 20844406483600.

The previous prime is 21365516645677. The next prime is 21365516645791. The reversal of 21365516645731 is 13754661556312.

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 21365516645731 - 2¹⁵ = 21365516612963 is a prime.

It is a super-2 number, since 2×21365516645731² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21365516645791) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 260555081005 + ... + 260555081086.

It is an arithmetic number, because the mean of its divisors is an integer number (5471656701966).

Almost surely, 2^{21365516645731} is an apocalyptic number.

21365516645731 is a deficient number, since it is larger than the sum of its proper divisors (521110162133).

21365516645731 is an equidigital number, since it uses as much as digits as its factorization.

21365516645731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 521110162132.

The product of its digits is 13608000, while the sum is 55.

The spelling of 21365516645731 in words is "twenty-one trillion, three hundred sixty-five billion, five hundred sixteen million, six hundred forty-five thousand, seven hundred thirty-one".