20785408561 has 2 divisors, whose sum is σ = 20785408562. Its totient is φ = 20785408560.

The previous prime is 20785408559. The next prime is 20785408619. The reversal of 20785408561 is 16580458702.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11955235600 + 8830172961 = 109340^2 + 93969^2 .

It is a cyclic number.

It is not a de Polignac number, because 20785408561 - 2¹ = 20785408559 is a prime.

Together with 20785408559, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (20785408261) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10392704280 + 10392704281.

It is an arithmetic number, because the mean of its divisors is an integer number (10392704281).

Almost surely, 2^20785408561 is an apocalyptic number.

It is an amenable number.

20785408561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20785408561 is an equidigital number, since it uses as much as digits as its factorization.

20785408561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 537600, while the sum is 46.

The spelling of 20785408561 in words is "twenty billion, seven hundred eighty-five million, four hundred eight thousand, five hundred sixty-one".