21211999 has 12 divisors (see below), whose sum is σ = 22747224. Its totient is φ = 19773072.

The previous prime is 21211997. The next prime is 21212017. The reversal of 21211999 is 99911212.

21211999 = T₇₆₂ + T₇₆₃ + ... + T₈₂₈.

It is not a de Polignac number, because 21211999 - 2¹ = 21211997 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21211997) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 23749 + ... + 24625.

It is an arithmetic number, because the mean of its divisors is an integer number (1895602).

Almost surely, 2^21211999 is an apocalyptic number.

21211999 is a deficient number, since it is larger than the sum of its proper divisors (1535225).

21211999 is an equidigital number, since it uses as much as digits as its factorization.

21211999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 982 (or 963 counting only the distinct ones).

The product of its digits is 2916, while the sum is 34.

The square root of 21211999 is about 4605.6485971033. The cubic root of 21211999 is about 276.8177064350.

The spelling of 21211999 in words is "twenty-one million, two hundred eleven thousand, nine hundred ninety-nine".