20491685681 has 2 divisors, whose sum is σ = 20491685682. Its totient is φ = 20491685680.

The previous prime is 20491685659. The next prime is 20491685699. The reversal of 20491685681 is 18658619402.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18376513600 + 2115172081 = 135560^2 + 45991^2 .

It is a cyclic number.

It is not a de Polignac number, because 20491685681 - 2²² = 20487491377 is a prime.

It is a super-2 number, since 2×20491685681² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (20491685281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10245842840 + 10245842841.

It is an arithmetic number, because the mean of its divisors is an integer number (10245842841).

Almost surely, 2^20491685681 is an apocalyptic number.

It is an amenable number.

20491685681 is a deficient number, since it is larger than the sum of its proper divisors (1).

20491685681 is an equidigital number, since it uses as much as digits as its factorization.

20491685681 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 829440, while the sum is 50.

The spelling of 20491685681 in words is "twenty billion, four hundred ninety-one million, six hundred eighty-five thousand, six hundred eighty-one".