21555993 has 8 divisors (see below), whose sum is σ = 28996128. Its totient is φ = 14243264.

The previous prime is 21555967. The next prime is 21556009. The reversal of 21555993 is 39955512.

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 21555993 - 2¹⁰ = 21554969 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21555923) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 31455 + ... + 32132.

It is an arithmetic number, because the mean of its divisors is an integer number (3624516).

Almost surely, 2^21555993 is an apocalyptic number.

It is an amenable number.

21555993 is a deficient number, since it is larger than the sum of its proper divisors (7440135).

21555993 is a wasteful number, since it uses less digits than its factorization.

21555993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 63703.

The product of its digits is 60750, while the sum is 39.

The square root of 21555993 is about 4642.8432021769. The cubic root of 21555993 is about 278.3060695762.

The spelling of 21555993 in words is "twenty-one million, five hundred fifty-five thousand, nine hundred ninety-three".