21989999 has 2 divisors, whose sum is σ = 21990000. Its totient is φ = 21989998.

The previous prime is 21989983. The next prime is 21990013. The reversal of 21989999 is 99998912.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21989999 - 2⁴ = 21989983 is a prime.

21989999 is a modest number, since divided by 9999 gives 2198 as remainder.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21989969) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10994999 + 10995000.

It is an arithmetic number, because the mean of its divisors is an integer number (10995000).

Almost surely, 2^21989999 is an apocalyptic number.

21989999 is a deficient number, since it is larger than the sum of its proper divisors (1).

21989999 is an equidigital number, since it uses as much as digits as its factorization.

21989999 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 944784, while the sum is 56.

The square root of 21989999 is about 4689.3495284527. The cubic root of 21989999 is about 280.1614672431.

It can be divided in two parts, 219 and 89999, that multiplied together give a triangular number (19709781 = T₆₂₇₈).

The spelling of 21989999 in words is "twenty-one million, nine hundred eighty-nine thousand, nine hundred ninety-nine".