21947939 has 8 divisors (see below), whose sum is σ = 23922192. Its totient is φ = 20014560.

The previous prime is 21947923. The next prime is 21947951. The reversal of 21947939 is 93974912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21947939 - 2⁴ = 21947923 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21947939.

It is not an unprimeable number, because it can be changed into a prime (21947339) 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 in 7 ways as a sum of consecutive naturals, for example, 9092 + ... + 11249.

It is an arithmetic number, because the mean of its divisors is an integer number (2990274).

Almost surely, 2^21947939 is an apocalyptic number.

21947939 is a deficient number, since it is larger than the sum of its proper divisors (1974253).

21947939 is a wasteful number, since it uses less digits than its factorization.

21947939 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20437.

The product of its digits is 122472, while the sum is 44.

The square root of 21947939 is about 4684.8627514581. The cubic root of 21947939 is about 279.9827327787.

The spelling of 21947939 in words is "twenty-one million, nine hundred forty-seven thousand, nine hundred thirty-nine".