121891209 has 16 divisors (see below), whose sum is σ = 182089920. Its totient is φ = 71876160.

The previous prime is 121891201. The next prime is 121891243. The reversal of 121891209 is 902198121.

It is not a de Polignac number, because 121891209 - 2³ = 121891201 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a self number, because there is not a number n which added to its sum of digits gives 121891209.

It is not an unprimeable number, because it can be changed into a prime (121891201) 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, 48694 + ... + 51135.

It is an arithmetic number, because the mean of its divisors is an integer number (11380620).

Almost surely, 2^121891209 is an apocalyptic number.

It is an amenable number.

121891209 is a deficient number, since it is larger than the sum of its proper divisors (60198711).

121891209 is a wasteful number, since it uses less digits than its factorization.

121891209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99880.

The product of its (nonzero) digits is 2592, while the sum is 33.

The square root of 121891209 is about 11040.4351816403. The cubic root of 121891209 is about 495.8200995707.

The spelling of 121891209 in words is "one hundred twenty-one million, eight hundred ninety-one thousand, two hundred nine".