20556555511 has 2 divisors, whose sum is σ = 20556555512. Its totient is φ = 20556555510.

The previous prime is 20556555433. The next prime is 20556555517. The reversal of 20556555511 is 11555565502.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20556555511 - 2¹¹ = 20556553463 is a prime.

It is a super-2 number, since 2×20556555511² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20556555517) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10278277755 + 10278277756.

It is an arithmetic number, because the mean of its divisors is an integer number (10278277756).

Almost surely, 2^20556555511 is an apocalyptic number.

20556555511 is a deficient number, since it is larger than the sum of its proper divisors (1).

20556555511 is an equidigital number, since it uses as much as digits as its factorization.

20556555511 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 187500, while the sum is 40.

Subtracting from 20556555511 its reverse (11555565502), we obtain a palindrome (9000990009).

The spelling of 20556555511 in words is "twenty billion, five hundred fifty-six million, five hundred fifty-five thousand, five hundred eleven".