21957993 has 16 divisors (see below), whose sum is σ = 33288640. Its totient is φ = 14297472.

The previous prime is 21957989. The next prime is 21957997. The reversal of 21957993 is 39975912.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21957989) and next prime (21957997).

It is not a de Polignac number, because 21957993 - 2² = 21957989 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 (21957997) 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 15 ways as a sum of consecutive naturals, for example, 8296 + ... + 10617.

It is an arithmetic number, because the mean of its divisors is an integer number (2080540).

Almost surely, 2^21957993 is an apocalyptic number.

It is an amenable number.

21957993 is a deficient number, since it is larger than the sum of its proper divisors (11330647).

21957993 is a wasteful number, since it uses less digits than its factorization.

21957993 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18965 (or 18959 counting only the distinct ones).

The product of its digits is 153090, while the sum is 45.

The square root of 21957993 is about 4685.9356589693. The cubic root of 21957993 is about 280.0254781238.

The spelling of 21957993 in words is "twenty-one million, nine hundred fifty-seven thousand, nine hundred ninety-three".