20561617243 has 2 divisors, whose sum is σ = 20561617244. Its totient is φ = 20561617242.

The previous prime is 20561617217. The next prime is 20561617247. The reversal of 20561617243 is 34271616502.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20561617243 is a prime.

It is not a weakly prime, because it can be changed into another prime (20561617247) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10280808621 + 10280808622.

It is an arithmetic number, because the mean of its divisors is an integer number (10280808622).

Almost surely, 2^20561617243 is an apocalyptic number.

20561617243 is a deficient number, since it is larger than the sum of its proper divisors (1).

20561617243 is an equidigital number, since it uses as much as digits as its factorization.

20561617243 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 60480, while the sum is 37.

The spelling of 20561617243 in words is "twenty billion, five hundred sixty-one million, six hundred seventeen thousand, two hundred forty-three".