21253015757 has 2 divisors, whose sum is σ = 21253015758. Its totient is φ = 21253015756.

The previous prime is 21253015643. The next prime is 21253015769. The reversal of 21253015757 is 75751035212.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18055565641 + 3197450116 = 134371^2 + 56546^2 .

It is a cyclic number.

It is not a de Polignac number, because 21253015757 - 2²⁰ = 21251967181 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21253015757.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21253015957) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10626507878 + 10626507879.

It is an arithmetic number, because the mean of its divisors is an integer number (10626507879).

Almost surely, 2^21253015757 is an apocalyptic number.

It is an amenable number.

21253015757 is a deficient number, since it is larger than the sum of its proper divisors (1).

21253015757 is an equidigital number, since it uses as much as digits as its factorization.

21253015757 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 38.

The spelling of 21253015757 in words is "twenty-one billion, two hundred fifty-three million, fifteen thousand, seven hundred fifty-seven".