20981999 has 2 divisors, whose sum is σ = 20982000. Its totient is φ = 20981998.

The previous prime is 20981971. The next prime is 20982001. The reversal of 20981999 is 99918902.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20981999 is a prime.

Together with 20982001, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20981929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10490999 + 10491000.

It is an arithmetic number, because the mean of its divisors is an integer number (10491000).

Almost surely, 2^20981999 is an apocalyptic number.

20981999 is a deficient number, since it is larger than the sum of its proper divisors (1).

20981999 is an equidigital number, since it uses as much as digits as its factorization.

20981999 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 104976, while the sum is 47.

The square root of 20981999 is about 4580.6112037587. The cubic root of 20981999 is about 275.8135643188.

The spelling of 20981999 in words is "twenty million, nine hundred eighty-one thousand, nine hundred ninety-nine".