21205530757 has 2 divisors, whose sum is σ = 21205530758. Its totient is φ = 21205530756.

The previous prime is 21205530739. The next prime is 21205530767. The reversal of 21205530757 is 75703550212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20072939041 + 1132591716 = 141679^2 + 33654^2 .

It is a cyclic number.

It is not a de Polignac number, because 21205530757 - 2⁷ = 21205530629 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21205530727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602765378 + 10602765379.

It is an arithmetic number, because the mean of its divisors is an integer number (10602765379).

Almost surely, 2^21205530757 is an apocalyptic number.

It is an amenable number.

21205530757 is a deficient number, since it is larger than the sum of its proper divisors (1).

21205530757 is an equidigital number, since it uses as much as digits as its factorization.

21205530757 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 73500, while the sum is 37.

The spelling of 21205530757 in words is "twenty-one billion, two hundred five million, five hundred thirty thousand, seven hundred fifty-seven".