121605721 has 4 divisors (see below), whose sum is σ = 122493492. Its totient is φ = 120717952.

The previous prime is 121605703. The next prime is 121605733. The reversal of 121605721 is 127506121.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 127506121 = 5693 ⋅22397.

It can be written as a sum of positive squares in 2 ways, for example, as 28772496 + 92833225 = 5364^2 + 9635^2 .

It is a cyclic number.

It is not a de Polignac number, because 121605721 - 2⁷ = 121605593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (121605751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 443680 + ... + 443953.

It is an arithmetic number, because the mean of its divisors is an integer number (30623373).

Almost surely, 2^121605721 is an apocalyptic number.

It is an amenable number.

121605721 is a deficient number, since it is larger than the sum of its proper divisors (887771).

121605721 is an equidigital number, since it uses as much as digits as its factorization.

121605721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 887770.

The product of its (nonzero) digits is 840, while the sum is 25.

The square root of 121605721 is about 11027.4984017228. The cubic root of 121605721 is about 495.4327012643.

The spelling of 121605721 in words is "one hundred twenty-one million, six hundred five thousand, seven hundred twenty-one".