121779991 has 4 divisors (see below), whose sum is σ = 121805712. Its totient is φ = 121754272.

The previous prime is 121779971. The next prime is 121780039. The reversal of 121779991 is 199977121.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199977121 = 127 ⋅1574623.

It is a cyclic number.

It is not a de Polignac number, because 121779991 - 2⁷ = 121779863 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (121779941) 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, 3475 + ... + 15988.

It is an arithmetic number, because the mean of its divisors is an integer number (30451428).

Almost surely, 2^121779991 is an apocalyptic number.

121779991 is a deficient number, since it is larger than the sum of its proper divisors (25721).

121779991 is an equidigital number, since it uses as much as digits as its factorization.

121779991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25720.

The product of its digits is 71442, while the sum is 46.

The square root of 121779991 is about 11035.3971836088. The cubic root of 121779991 is about 495.6692522136.

The spelling of 121779991 in words is "one hundred twenty-one million, seven hundred seventy-nine thousand, nine hundred ninety-one".