21215571561161 has 8 divisors (see below), whose sum is σ = 21563442396744. Its totient is φ = 20867703131520.

The previous prime is 21215571561139. The next prime is 21215571561221. The reversal of 21215571561161 is 16116517551212.

It can be written as a sum of positive squares in 4 ways, for example, as 3152595558025 + 18062976003136 = 1775555^2 + 4250056^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21215571561161 - 2¹⁸ = 21215571299017 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21215571561101) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 29123771 + ... + 29843343.

It is an arithmetic number, because the mean of its divisors is an integer number (2695430299593).

Almost surely, 2^{21215571561161} is an apocalyptic number.

It is an amenable number.

21215571561161 is a deficient number, since it is larger than the sum of its proper divisors (347870835583).

21215571561161 is an equidigital number, since it uses as much as digits as its factorization.

21215571561161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1202971.

The product of its digits is 126000, while the sum is 44.

The spelling of 21215571561161 in words is "twenty-one trillion, two hundred fifteen billion, five hundred seventy-one million, five hundred sixty-one thousand, one hundred sixty-one".