1561720717121 has 4 divisors (see below), whose sum is σ = 1561723626672. Its totient is φ = 1561717807572.

The previous prime is 1561720717103. The next prime is 1561720717229. The reversal of 1561720717121 is 1217170271651.

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 1561720717121 - 2¹⁴ = 1561720700737 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1561720717621) 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, 389735 + ... + 1809788.

It is an arithmetic number, because the mean of its divisors is an integer number (390430906668).

Almost surely, 2^{1561720717121} is an apocalyptic number.

It is an amenable number.

1561720717121 is a deficient number, since it is larger than the sum of its proper divisors (2909551).

1561720717121 is an equidigital number, since it uses as much as digits as its factorization.

1561720717121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2909550.

The product of its (nonzero) digits is 41160, while the sum is 41.

Adding to 1561720717121 its reverse (1217170271651), we get a palindrome (2778890988772).

The spelling of 1561720717121 in words is "one trillion, five hundred sixty-one billion, seven hundred twenty million, seven hundred seventeen thousand, one hundred twenty-one".