20404255561 has 2 divisors, whose sum is σ = 20404255562. Its totient is φ = 20404255560.

The previous prime is 20404255549. The next prime is 20404255567. The reversal of 20404255561 is 16555240402.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19489556025 + 914699536 = 139605^2 + 30244^2 .

It is a cyclic number.

It is not a de Polignac number, because 20404255561 - 2¹⁵ = 20404222793 is a prime.

It is not a weakly prime, because it can be changed into another prime (20404255567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10202127780 + 10202127781.

It is an arithmetic number, because the mean of its divisors is an integer number (10202127781).

Almost surely, 2^20404255561 is an apocalyptic number.

It is an amenable number.

20404255561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20404255561 is an equidigital number, since it uses as much as digits as its factorization.

20404255561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 48000, while the sum is 34.

Adding to 20404255561 its reverse (16555240402), we get a palindrome (36959495963).

The spelling of 20404255561 in words is "twenty billion, four hundred four million, two hundred fifty-five thousand, five hundred sixty-one".