21566943613 has 2 divisors, whose sum is σ = 21566943614. Its totient is φ = 21566943612.

The previous prime is 21566943569. The next prime is 21566943659. The reversal of 21566943613 is 31634966512.

It is an a-pointer prime, because the next prime (21566943659) can be obtained adding 21566943613 to its sum of digits (46).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20472458724 + 1094484889 = 143082^2 + 33083^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21566943613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21566943683) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10783471806 + 10783471807.

It is an arithmetic number, because the mean of its divisors is an integer number (10783471807).

Almost surely, 2^21566943613 is an apocalyptic number.

It is an amenable number.

21566943613 is a deficient number, since it is larger than the sum of its proper divisors (1).

21566943613 is an equidigital number, since it uses as much as digits as its factorization.

21566943613 is an evil number, because the sum of its binary digits is even.

The product of its digits is 699840, while the sum is 46.

The spelling of 21566943613 in words is "twenty-one billion, five hundred sixty-six million, nine hundred forty-three thousand, six hundred thirteen".