21656166001 has 4 divisors (see below), whose sum is σ = 21658653412. Its totient is φ = 21653678592.

The previous prime is 21656165953. The next prime is 21656166019. The reversal of 21656166001 is 10066165612.

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 13986610225 + 7669555776 = 118265^2 + 87576^2 .

It is a cyclic number.

It is not a de Polignac number, because 21656166001 - 2¹¹ = 21656163953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21656166041) 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, 1230600 + ... + 1248073.

It is an arithmetic number, because the mean of its divisors is an integer number (5414663353).

Almost surely, 2^21656166001 is an apocalyptic number.

It is an amenable number.

21656166001 is a deficient number, since it is larger than the sum of its proper divisors (2487411).

21656166001 is an equidigital number, since it uses as much as digits as its factorization.

21656166001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2487410.

The product of its (nonzero) digits is 12960, while the sum is 34.

The spelling of 21656166001 in words is "twenty-one billion, six hundred fifty-six million, one hundred sixty-six thousand, one".