21366747581 has 2 divisors, whose sum is σ = 21366747582. Its totient is φ = 21366747580.

The previous prime is 21366747569. The next prime is 21366747599. The reversal of 21366747581 is 18574766312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18179128900 + 3187618681 = 134830^2 + 56459^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21366747581 is a prime.

It is a super-3 number, since 3×21366747581³ (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21366747511) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10683373790 + 10683373791.

It is an arithmetic number, because the mean of its divisors is an integer number (10683373791).

Almost surely, 2^21366747581 is an apocalyptic number.

It is an amenable number.

21366747581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21366747581 is an equidigital number, since it uses as much as digits as its factorization.

21366747581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1693440, while the sum is 50.

The spelling of 21366747581 in words is "twenty-one billion, three hundred sixty-six million, seven hundred forty-seven thousand, five hundred eighty-one".