1561118821 has 2 divisors, whose sum is σ = 1561118822. Its totient is φ = 1561118820.

The previous prime is 1561118791. The next prime is 1561118833. The reversal of 1561118821 is 1288111651.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1519050625 + 42068196 = 38975^2 + 6486^2 .

It is an emirp because it is prime and its reverse (1288111651) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1561118821 - 2¹¹ = 1561116773 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1561118621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780559410 + 780559411.

It is an arithmetic number, because the mean of its divisors is an integer number (780559411).

Almost surely, 2^1561118821 is an apocalyptic number.

It is an amenable number.

1561118821 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561118821 is an equidigital number, since it uses as much as digits as its factorization.

1561118821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3840, while the sum is 34.

The square root of 1561118821 is about 39510.9962035887. The cubic root of 1561118821 is about 1160.0551948073.

The spelling of 1561118821 in words is "one billion, five hundred sixty-one million, one hundred eighteen thousand, eight hundred twenty-one".