21707993 has 4 divisors (see below), whose sum is σ = 21725748. Its totient is φ = 21690240.

The previous prime is 21707981. The next prime is 21707999. The reversal of 21707993 is 39970712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 20912329 + 795664 = 4573^2 + 892^2 .

It is a cyclic number.

It is not a de Polignac number, because 21707993 - 2⁴ = 21707977 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21707999) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6896 + ... + 9537.

It is an arithmetic number, because the mean of its divisors is an integer number (5431437).

Almost surely, 2^21707993 is an apocalyptic number.

It is an amenable number.

21707993 is a deficient number, since it is larger than the sum of its proper divisors (17755).

21707993 is a wasteful number, since it uses less digits than its factorization.

21707993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17754.

The product of its (nonzero) digits is 23814, while the sum is 38.

The square root of 21707993 is about 4659.1837267916. The cubic root of 21707993 is about 278.9586874592.

The spelling of 21707993 in words is "twenty-one million, seven hundred seven thousand, nine hundred ninety-three".