21121909 has 2 divisors, whose sum is σ = 21121910. Its totient is φ = 21121908.

The previous prime is 21121883. The next prime is 21121913. The reversal of 21121909 is 90912112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13950225 + 7171684 = 3735^2 + 2678^2 .

It is a cyclic number.

It is not a de Polignac number, because 21121909 - 2⁷ = 21121781 is a prime.

It is a super-2 number, since 2×21121909² = 892270079608562, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21121949) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10560954 + 10560955.

It is an arithmetic number, because the mean of its divisors is an integer number (10560955).

Almost surely, 2^21121909 is an apocalyptic number.

It is an amenable number.

21121909 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121909 is an equidigital number, since it uses as much as digits as its factorization.

21121909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 324, while the sum is 25.

The square root of 21121909 is about 4595.8578089406. The cubic root of 21121909 is about 276.4252572311.

The spelling of 21121909 in words is "twenty-one million, one hundred twenty-one thousand, nine hundred nine".