21931686661 has 2 divisors, whose sum is σ = 21931686662. Its totient is φ = 21931686660.

The previous prime is 21931686649. The next prime is 21931686701. The reversal of 21931686661 is 16668613912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15879780225 + 6051906436 = 126015^2 + 77794^2 .

It is a cyclic number.

It is not a de Polignac number, because 21931686661 - 2¹¹ = 21931684613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21931683661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10965843330 + 10965843331.

It is an arithmetic number, because the mean of its divisors is an integer number (10965843331).

Almost surely, 2^21931686661 is an apocalyptic number.

It is an amenable number.

21931686661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21931686661 is an equidigital number, since it uses as much as digits as its factorization.

21931686661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 559872, while the sum is 49.

The spelling of 21931686661 in words is "twenty-one billion, nine hundred thirty-one million, six hundred eighty-six thousand, six hundred sixty-one".