21215939 has 2 divisors, whose sum is σ = 21215940. Its totient is φ = 21215938.

The previous prime is 21215921. The next prime is 21215963. The reversal of 21215939 is 93951212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21215939 - 2²⁰ = 20167363 is a prime.

It is not a weakly prime, because it can be changed into another prime (21215969) 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, 10607969 + 10607970.

It is an arithmetic number, because the mean of its divisors is an integer number (10607970).

Almost surely, 2^21215939 is an apocalyptic number.

21215939 is a deficient number, since it is larger than the sum of its proper divisors (1).

21215939 is an equidigital number, since it uses as much as digits as its factorization.

21215939 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4860, while the sum is 32.

The square root of 21215939 is about 4606.0763128719. The cubic root of 21215939 is about 276.8348444432.

The spelling of 21215939 in words is "twenty-one million, two hundred fifteen thousand, nine hundred thirty-nine".