1561672121 has 4 divisors (see below), whose sum is σ = 1588141200. Its totient is φ = 1535203044.

The previous prime is 1561672117. The next prime is 1561672157. The reversal of 1561672121 is 1212761651.

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.

It is a cyclic number.

It is not a de Polignac number, because 1561672121 - 2² = 1561672117 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1561672181) 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, 13234451 + ... + 13234568.

It is an arithmetic number, because the mean of its divisors is an integer number (397035300).

Almost surely, 2^1561672121 is an apocalyptic number.

It is an amenable number.

1561672121 is a deficient number, since it is larger than the sum of its proper divisors (26469079).

1561672121 is an equidigital number, since it uses as much as digits as its factorization.

1561672121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26469078.

The product of its digits is 5040, while the sum is 32.

The square root of 1561672121 is about 39517.9974315501. The cubic root of 1561672121 is about 1160.1922295876.

The spelling of 1561672121 in words is "one billion, five hundred sixty-one million, six hundred seventy-two thousand, one hundred twenty-one".