21757215817 has 2 divisors, whose sum is σ = 21757215818. Its totient is φ = 21757215816.

The previous prime is 21757215803. The next prime is 21757215833. The reversal of 21757215817 is 71851275712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11634642496 + 10122573321 = 107864^2 + 100611^2 .

It is a cyclic number.

It is not a de Polignac number, because 21757215817 - 2¹¹ = 21757213769 is a prime.

It is not a weakly prime, because it can be changed into another prime (21757215877) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10878607908 + 10878607909.

It is an arithmetic number, because the mean of its divisors is an integer number (10878607909).

Almost surely, 2^21757215817 is an apocalyptic number.

It is an amenable number.

21757215817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21757215817 is an equidigital number, since it uses as much as digits as its factorization.

21757215817 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 274400, while the sum is 46.

The spelling of 21757215817 in words is "twenty-one billion, seven hundred fifty-seven million, two hundred fifteen thousand, eight hundred seventeen".