20997989 has 2 divisors, whose sum is σ = 20997990. Its totient is φ = 20997988.

The previous prime is 20997973. The next prime is 20998007. The reversal of 20997989 is 98979902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11847364 + 9150625 = 3442^2 + 3025^2 .

It is a cyclic number.

It is not a de Polignac number, because 20997989 - 2⁴ = 20997973 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20997989.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20991989) 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, 10498994 + 10498995.

It is an arithmetic number, because the mean of its divisors is an integer number (10498995).

Almost surely, 2^20997989 is an apocalyptic number.

It is an amenable number.

20997989 is a deficient number, since it is larger than the sum of its proper divisors (1).

20997989 is an equidigital number, since it uses as much as digits as its factorization.

20997989 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 734832, while the sum is 53.

The square root of 20997989 is about 4582.3562716140. The cubic root of 20997989 is about 275.8836106958.

The spelling of 20997989 in words is "twenty million, nine hundred ninety-seven thousand, nine hundred eighty-nine".