121557621665 has 4 divisors (see below), whose sum is σ = 145869146004. Its totient is φ = 97246097328.

The previous prime is 121557621641. The next prime is 121557621667. The reversal of 121557621665 is 566126755121.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 566126755121 = 31 ⋅18262153391.

It can be written as a sum of positive squares in 2 ways, for example, as 45019079329 + 76538542336 = 212177^2 + 276656^2 .

It is a cyclic number.

It is not a de Polignac number, because 121557621665 - 2²² = 121553427361 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (121557621667) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12155762162 + ... + 12155762171.

It is an arithmetic number, because the mean of its divisors is an integer number (36467286501).

Almost surely, 2^121557621665 is an apocalyptic number.

It is an amenable number.

121557621665 is a deficient number, since it is larger than the sum of its proper divisors (24311524339).

121557621665 is an equidigital number, since it uses as much as digits as its factorization.

121557621665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24311524338.

The product of its digits is 756000, while the sum is 47.

The spelling of 121557621665 in words is "one hundred twenty-one billion, five hundred fifty-seven million, six hundred twenty-one thousand, six hundred sixty-five".