1121805721 has 4 divisors (see below), whose sum is σ = 1123717392. Its totient is φ = 1119894052.

The previous prime is 1121805719. The next prime is 1121805739. The reversal of 1121805721 is 1275081211.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1275081211 = 6679 ⋅190909.

It is a cyclic number.

It is not a de Polignac number, because 1121805721 - 2¹ = 1121805719 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1121805721.

It is not an unprimeable number, because it can be changed into a prime (1121805781) 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, 954955 + ... + 956128.

It is an arithmetic number, because the mean of its divisors is an integer number (280929348).

Almost surely, 2^1121805721 is an apocalyptic number.

It is an amenable number.

1121805721 is a deficient number, since it is larger than the sum of its proper divisors (1911671).

1121805721 is an equidigital number, since it uses as much as digits as its factorization.

1121805721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1911670.

The product of its (nonzero) digits is 1120, while the sum is 28.

The square root of 1121805721 is about 33493.3683137423. The cubic root of 1121805721 is about 1039.0566275859.

Adding to 1121805721 its reverse (1275081211), we get a palindrome (2396886932).

The spelling of 1121805721 in words is "one billion, one hundred twenty-one million, eight hundred five thousand, seven hundred twenty-one".