21166305811661 has 4 divisors (see below), whose sum is σ = 21616652743872. Its totient is φ = 20715958879452.

The previous prime is 21166305811627. The next prime is 21166305811687. The reversal of 21166305811661 is 16611850366112.

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 21166305811661 - 2¹⁴ = 21166305795277 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (47), and also a Moran number because the ratio is a prime number: 450346932163 = 21166305811661 / (2 + 1 + 1 + 6 + 6 + 3 + 0 + 5 + 8 + 1 + 1 + 6 + 6 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21166305811691) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 225173466035 + ... + 225173466128.

It is an arithmetic number, because the mean of its divisors is an integer number (5404163185968).

Almost surely, 2^{21166305811661} is an apocalyptic number.

It is an amenable number.

21166305811661 is a deficient number, since it is larger than the sum of its proper divisors (450346932211).

21166305811661 is an equidigital number, since it uses as much as digits as its factorization.

21166305811661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 450346932210.

The product of its (nonzero) digits is 311040, while the sum is 47.

The spelling of 21166305811661 in words is "twenty-one trillion, one hundred sixty-six billion, three hundred five million, eight hundred eleven thousand, six hundred sixty-one".