21971399 has 2 divisors, whose sum is σ = 21971400. Its totient is φ = 21971398.

The previous prime is 21971393. The next prime is 21971413. The reversal of 21971399 is 99317912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21971399 - 2⁸ = 21971143 is a prime.

It is a Sophie Germain 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 (21971393) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10985699 + 10985700.

It is an arithmetic number, because the mean of its divisors is an integer number (10985700).

Almost surely, 2^21971399 is an apocalyptic number.

21971399 is a deficient number, since it is larger than the sum of its proper divisors (1).

21971399 is an equidigital number, since it uses as much as digits as its factorization.

21971399 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 30618, while the sum is 41.

The square root of 21971399 is about 4687.3658914149. The cubic root of 21971399 is about 280.0824544579.

The spelling of 21971399 in words is "twenty-one million, nine hundred seventy-one thousand, three hundred ninety-nine".