20731611661 has 4 divisors (see below), whose sum is σ = 20839029532. Its totient is φ = 20624193792.

The previous prime is 20731611643. The next prime is 20731611679. The reversal of 20731611661 is 16611613702.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (20731611643) and next prime (20731611679).

It can be written as a sum of positive squares in 2 ways, for example, as 11089353636 + 9642258025 = 105306^2 + 98195^2 .

It is a cyclic number.

It is not a de Polignac number, because 20731611661 - 2⁹ = 20731611149 is a prime.

It is a super-2 number, since 2×20731611661² (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 (20731611631) 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 in 3 ways as a sum of consecutive naturals, for example, 53708646 + ... + 53709031.

It is an arithmetic number, because the mean of its divisors is an integer number (5209757383).

Almost surely, 2^20731611661 is an apocalyptic number.

It is an amenable number.

20731611661 is a deficient number, since it is larger than the sum of its proper divisors (107417871).

20731611661 is a wasteful number, since it uses less digits than its factorization.

20731611661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 107417870.

The product of its (nonzero) digits is 9072, while the sum is 34.

The spelling of 20731611661 in words is "twenty billion, seven hundred thirty-one million, six hundred eleven thousand, six hundred sixty-one".