20691061681 has 4 divisors (see below), whose sum is σ = 21195721764. Its totient is φ = 20186401600.

The previous prime is 20691061663. The next prime is 20691061711. The reversal of 20691061681 is 18616019602.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18616019602 = 2 ⋅9308009801.

It can be written as a sum of positive squares in 2 ways, for example, as 770562081 + 19920499600 = 27759^2 + 141140^2 .

It is a cyclic number.

It is not a de Polignac number, because 20691061681 - 2⁹ = 20691061169 is a prime.

It is a super-2 number, since 2×20691061681² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20691061621) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 252329980 + ... + 252330061.

It is an arithmetic number, because the mean of its divisors is an integer number (5298930441).

Almost surely, 2^20691061681 is an apocalyptic number.

It is an amenable number.

20691061681 is a deficient number, since it is larger than the sum of its proper divisors (504660083).

20691061681 is an equidigital number, since it uses as much as digits as its factorization.

20691061681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 504660082.

The product of its (nonzero) digits is 31104, while the sum is 40.

The spelling of 20691061681 in words is "twenty billion, six hundred ninety-one million, sixty-one thousand, six hundred eighty-one".