21191558121 has 16 divisors (see below), whose sum is σ = 31421531520. Its totient is φ = 14115721680.

The previous prime is 21191558077. The next prime is 21191558123. The reversal of 21191558121 is 12185519112.

It is a happy number.

21191558121 is a `hidden beast` number, since 2 + 1 + 1 + 91 + 558 + 12 + 1 = 666.

It is not a de Polignac number, because 21191558121 - 2³⁰ = 20117816297 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21191558123) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 300405 + ... + 364178.

It is an arithmetic number, because the mean of its divisors is an integer number (1963845720).

Almost surely, 2^21191558121 is an apocalyptic number.

It is an amenable number.

21191558121 is a deficient number, since it is larger than the sum of its proper divisors (10229973399).

21191558121 is a wasteful number, since it uses less digits than its factorization.

21191558121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 665773 (or 665767 counting only the distinct ones).

The product of its digits is 7200, while the sum is 36.

The spelling of 21191558121 in words is "twenty-one billion, one hundred ninety-one million, five hundred fifty-eight thousand, one hundred twenty-one".