20561561 has 2 divisors, whose sum is σ = 20561562. Its totient is φ = 20561560.

The previous prime is 20561549. The next prime is 20561573. The reversal of 20561561 is 16516502.

It is a balanced prime because it is at equal distance from previous prime (20561549) and next prime (20561573).

It can be written as a sum of positive squares in only one way, i.e., 10758400 + 9803161 = 3280^2 + 3131^2 .

It is a cyclic number.

It is not a de Polignac number, because 20561561 - 2¹⁰ = 20560537 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20561561.

It is not a weakly prime, because it can be changed into another prime (20561501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10280780 + 10280781.

It is an arithmetic number, because the mean of its divisors is an integer number (10280781).

Almost surely, 2^20561561 is an apocalyptic number.

It is an amenable number.

20561561 is a deficient number, since it is larger than the sum of its proper divisors (1).

20561561 is an equidigital number, since it uses as much as digits as its factorization.

20561561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 20561561 is about 4534.4857481307. The cubic root of 20561561 is about 273.9588666120.

The spelling of 20561561 in words is "twenty million, five hundred sixty-one thousand, five hundred sixty-one".