21665564033545 has 4 divisors (see below), whose sum is σ = 25998676840260. Its totient is φ = 17332451226832.

The previous prime is 21665564033489. The next prime is 21665564033573. The reversal of 21665564033545 is 54533046556612.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10330329530889 + 11335234502656 = 3214083^2 + 3366784^2 .

It is a cyclic number.

It is not a de Polignac number, because 21665564033545 - 2¹⁵ = 21665564000777 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2166556403350 + ... + 2166556403359.

It is an arithmetic number, because the mean of its divisors is an integer number (6499669210065).

Almost surely, 2^{21665564033545} is an apocalyptic number.

It is an amenable number.

21665564033545 is a deficient number, since it is larger than the sum of its proper divisors (4333112806715).

21665564033545 is an equidigital number, since it uses as much as digits as its factorization.

21665564033545 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4333112806714.

The product of its (nonzero) digits is 38880000, while the sum is 55.

The spelling of 21665564033545 in words is "twenty-one trillion, six hundred sixty-five billion, five hundred sixty-four million, thirty-three thousand, five hundred forty-five".