20781568776641 has 2 divisors, whose sum is σ = 20781568776642. Its totient is φ = 20781568776640.

The previous prime is 20781568776589. The next prime is 20781568776643. The reversal of 20781568776641 is 14667786518702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12586494585025 + 8195074191616 = 3547745^2 + 2862704^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20781568776641 is a prime.

Together with 20781568776643, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20781568776643) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10390784388320 + 10390784388321.

It is an arithmetic number, because the mean of its divisors is an integer number (10390784388321).

Almost surely, 2^{20781568776641} is an apocalyptic number.

It is an amenable number.

20781568776641 is a deficient number, since it is larger than the sum of its proper divisors (1).

20781568776641 is an equidigital number, since it uses as much as digits as its factorization.

20781568776641 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 189665280, while the sum is 68.

The spelling of 20781568776641 in words is "twenty trillion, seven hundred eighty-one billion, five hundred sixty-eight million, seven hundred seventy-six thousand, six hundred forty-one".