20518612561 has 2 divisors, whose sum is σ = 20518612562. Its totient is φ = 20518612560.

The previous prime is 20518612559. The next prime is 20518612571. The reversal of 20518612561 is 16521681502.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20414980161 + 103632400 = 142881^2 + 10180^2 .

It is a cyclic number.

It is not a de Polignac number, because 20518612561 - 2¹ = 20518612559 is a prime.

It is a super-2 number, since 2×20518612561² (a number of 21 digits) contains 22 as substring.

Together with 20518612559, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 20518612561.

It is not a weakly prime, because it can be changed into another prime (20518612531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10259306280 + 10259306281.

It is an arithmetic number, because the mean of its divisors is an integer number (10259306281).

Almost surely, 2^20518612561 is an apocalyptic number.

It is an amenable number.

20518612561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20518612561 is an equidigital number, since it uses as much as digits as its factorization.

20518612561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 28800, while the sum is 37.

The spelling of 20518612561 in words is "twenty billion, five hundred eighteen million, six hundred twelve thousand, five hundred sixty-one".