19561031821 has 2 divisors, whose sum is σ = 19561031822. Its totient is φ = 19561031820.

The previous prime is 19561031813. The next prime is 19561031843. The reversal of 19561031821 is 12813016591.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18558612900 + 1002418921 = 136230^2 + 31661^2 .

It is a cyclic number.

It is not a de Polignac number, because 19561031821 - 2³ = 19561031813 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19561031851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9780515910 + 9780515911.

It is an arithmetic number, because the mean of its divisors is an integer number (9780515911).

Almost surely, 2^19561031821 is an apocalyptic number.

It is an amenable number.

19561031821 is a deficient number, since it is larger than the sum of its proper divisors (1).

19561031821 is an equidigital number, since it uses as much as digits as its factorization.

19561031821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12960, while the sum is 37.

The spelling of 19561031821 in words is "nineteen billion, five hundred sixty-one million, thirty-one thousand, eight hundred twenty-one".