20997491 has 2 divisors, whose sum is σ = 20997492. Its totient is φ = 20997490.

The previous prime is 20997467. The next prime is 20997511. The reversal of 20997491 is 19479902.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20997491 - 2¹⁰ = 20996467 is a prime.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (20997461) 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, 10498745 + 10498746.

It is an arithmetic number, because the mean of its divisors is an integer number (10498746).

Almost surely, 2^20997491 is an apocalyptic number.

20997491 is a deficient number, since it is larger than the sum of its proper divisors (1).

20997491 is an equidigital number, since it uses as much as digits as its factorization.

20997491 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 40824, while the sum is 41.

The square root of 20997491 is about 4582.3019324353. The cubic root of 20997491 is about 275.8814296755.

The spelling of 20997491 in words is "twenty million, nine hundred ninety-seven thousand, four hundred ninety-one".