21109939 has 2 divisors, whose sum is σ = 21109940. Its totient is φ = 21109938.

The previous prime is 21109927. The next prime is 21109973. The reversal of 21109939 is 93990112.

It is an a-pointer prime, because the next prime (21109973) can be obtained adding 21109939 to its sum of digits (34).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21109939 - 2¹³ = 21101747 is a prime.

It is not a weakly prime, because it can be changed into another prime (21109139) 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, 10554969 + 10554970.

It is an arithmetic number, because the mean of its divisors is an integer number (10554970).

Almost surely, 2^21109939 is an apocalyptic number.

21109939 is a deficient number, since it is larger than the sum of its proper divisors (1).

21109939 is an equidigital number, since it uses as much as digits as its factorization.

21109939 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4374, while the sum is 34.

The square root of 21109939 is about 4594.5553647769. Note that the first 3 decimals coincide. The cubic root of 21109939 is about 276.3730296985.

The spelling of 21109939 in words is "twenty-one million, one hundred nine thousand, nine hundred thirty-nine".