21557306791 has 2 divisors, whose sum is σ = 21557306792. Its totient is φ = 21557306790.

The previous prime is 21557306753. The next prime is 21557306833. The reversal of 21557306791 is 19760375512.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21557306791 - 2³¹ = 19409823143 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21557306711) 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 as a sum of consecutive naturals, namely, 10778653395 + 10778653396.

It is an arithmetic number, because the mean of its divisors is an integer number (10778653396).

Almost surely, 2^21557306791 is an apocalyptic number.

21557306791 is a deficient number, since it is larger than the sum of its proper divisors (1).

21557306791 is an equidigital number, since it uses as much as digits as its factorization.

21557306791 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 396900, while the sum is 46.

The spelling of 21557306791 in words is "twenty-one billion, five hundred fifty-seven million, three hundred six thousand, seven hundred ninety-one".