20556815557 has 2 divisors, whose sum is σ = 20556815558. Its totient is φ = 20556815556.

The previous prime is 20556815509. The next prime is 20556815563. The reversal of 20556815557 is 75551865502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19803807076 + 753008481 = 140726^2 + 27441^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20556815557 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20556815557.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20556815507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10278407778 + 10278407779.

It is an arithmetic number, because the mean of its divisors is an integer number (10278407779).

Almost surely, 2^20556815557 is an apocalyptic number.

It is an amenable number.

20556815557 is a deficient number, since it is larger than the sum of its proper divisors (1).

20556815557 is an equidigital number, since it uses as much as digits as its factorization.

20556815557 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2100000, while the sum is 49.

The spelling of 20556815557 in words is "twenty billion, five hundred fifty-six million, eight hundred fifteen thousand, five hundred fifty-seven".