21305947 has 24 divisors (see below), whose sum is σ = 25065936. Its totient is φ = 17991168.

The previous prime is 21305939. The next prime is 21305983. The reversal of 21305947 is 74950312.

It is not a de Polignac number, because 21305947 - 2³ = 21305939 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 (21305917) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 199068 + ... + 199174.

It is an arithmetic number, because the mean of its divisors is an integer number (1044414).

Almost surely, 2^21305947 is an apocalyptic number.

21305947 is a deficient number, since it is larger than the sum of its proper divisors (3759989).

21305947 is a wasteful number, since it uses less digits than its factorization.

21305947 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 207 (or 190 counting only the distinct ones).

The product of its (nonzero) digits is 7560, while the sum is 31.

The square root of 21305947 is about 4615.8365438997. The cubic root of 21305947 is about 277.2257800263.

The spelling of 21305947 in words is "twenty-one million, three hundred five thousand, nine hundred forty-seven".