20561999 has 2 divisors, whose sum is σ = 20562000. Its totient is φ = 20561998.

The previous prime is 20561927. The next prime is 20562011. The reversal of 20561999 is 99916502.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20561999 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20561599) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10280999 + 10281000.

It is an arithmetic number, because the mean of its divisors is an integer number (10281000).

Almost surely, 2^20561999 is an apocalyptic number.

20561999 is a deficient number, since it is larger than the sum of its proper divisors (1).

20561999 is an equidigital number, since it uses as much as digits as its factorization.

20561999 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 43740, while the sum is 41.

The square root of 20561999 is about 4534.5340444196. The cubic root of 20561999 is about 273.9608118782.

The spelling of 20561999 in words is "twenty million, five hundred sixty-one thousand, nine hundred ninety-nine".