20551561 has 2 divisors, whose sum is σ = 20551562. Its totient is φ = 20551560.

The previous prime is 20551523. The next prime is 20551577. The reversal of 20551561 is 16515502.

20551561 is nontrivially palindromic in base 8.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11431161 + 9120400 = 3381^2 + 3020^2 .

It is a cyclic number.

It is not a de Polignac number, because 20551561 - 2¹¹ = 20549513 is a prime.

It is not a weakly prime, because it can be changed into another prime (20551511) 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, 10275780 + 10275781.

It is an arithmetic number, because the mean of its divisors is an integer number (10275781).

Almost surely, 2^20551561 is an apocalyptic number.

It is an amenable number.

20551561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20551561 is an equidigital number, since it uses as much as digits as its factorization.

20551561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1500, while the sum is 25.

The square root of 20551561 is about 4533.3829531598. The cubic root of 20551561 is about 273.9144466234.

It can be divided in two parts, 20551 and 561, that added together give a palindrome (21112).

The spelling of 20551561 in words is "twenty million, five hundred fifty-one thousand, five hundred sixty-one".