20521537657 has 2 divisors, whose sum is σ = 20521537658. Its totient is φ = 20521537656.

The previous prime is 20521537649. The next prime is 20521537691. The reversal of 20521537657 is 75673512502.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10891844496 + 9629693161 = 104364^2 + 98131^2 .

It is a cyclic number.

It is not a de Polignac number, because 20521537657 - 2³ = 20521537649 is a prime.

It is a super-2 number, since 2×20521537657² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (20521517657) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10260768828 + 10260768829.

It is an arithmetic number, because the mean of its divisors is an integer number (10260768829).

Almost surely, 2^20521537657 is an apocalyptic number.

It is an amenable number.

20521537657 is a deficient number, since it is larger than the sum of its proper divisors (1).

20521537657 is an equidigital number, since it uses as much as digits as its factorization.

20521537657 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 441000, while the sum is 43.

The spelling of 20521537657 in words is "twenty billion, five hundred twenty-one million, five hundred thirty-seven thousand, six hundred fifty-seven".