1611115721 has 4 divisors (see below), whose sum is σ = 1705887252. Its totient is φ = 1516344192.

The previous prime is 1611115711. The next prime is 1611115729. The reversal of 1611115721 is 1275111161.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1275111161 = 883 ⋅1444067.

It can be written as a sum of positive squares in 2 ways, for example, as 1113156496 + 497959225 = 33364^2 + 22315^2 .

It is a cyclic number.

It is not a de Polignac number, because 1611115721 - 2³⁰ = 537373897 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1611115729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 47385740 + ... + 47385773.

It is an arithmetic number, because the mean of its divisors is an integer number (426471813).

Almost surely, 2^1611115721 is an apocalyptic number.

It is an amenable number.

1611115721 is a deficient number, since it is larger than the sum of its proper divisors (94771531).

1611115721 is an equidigital number, since it uses as much as digits as its factorization.

1611115721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94771530.

The product of its digits is 420, while the sum is 26.

The square root of 1611115721 is about 40138.7060204985. The cubic root of 1611115721 is about 1172.3093941111.

Adding to 1611115721 its reverse (1275111161), we get a palindrome (2886226882).

The spelling of 1611115721 in words is "one billion, six hundred eleven million, one hundred fifteen thousand, seven hundred twenty-one".