20666568781 has 8 divisors (see below), whose sum is σ = 21226934520. Its totient is φ = 20106298368.

The previous prime is 20666568751. The next prime is 20666568799. The reversal of 20666568781 is 18786566602.

It can be written as a sum of positive squares in 4 ways, for example, as 9317075625 + 11349493156 = 96525^2 + 106534^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20666568781 - 2¹³ = 20666560589 is a prime.

It is a super-2 number, since 2×20666568781² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20666568701) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 759825 + ... + 786553.

It is an arithmetic number, because the mean of its divisors is an integer number (2653366815).

Almost surely, 2^20666568781 is an apocalyptic number.

It is an amenable number.

20666568781 is a deficient number, since it is larger than the sum of its proper divisors (560365739).

20666568781 is a wasteful number, since it uses less digits than its factorization.

20666568781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 47663.

The product of its (nonzero) digits is 5806080, while the sum is 55.

The spelling of 20666568781 in words is "twenty billion, six hundred sixty-six million, five hundred sixty-eight thousand, seven hundred eighty-one".