21555983 has 4 divisors (see below), whose sum is σ = 22824000. Its totient is φ = 20287968.

The previous prime is 21555967. The next prime is 21556009. The reversal of 21555983 is 38955512.

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

It is a cyclic number.

It is not a de Polignac number, because 21555983 - 2⁴ = 21555967 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 (21555923) 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 3 ways as a sum of consecutive naturals, for example, 633983 + ... + 634016.

It is an arithmetic number, because the mean of its divisors is an integer number (5706000).

Almost surely, 2^21555983 is an apocalyptic number.

21555983 is a deficient number, since it is larger than the sum of its proper divisors (1268017).

21555983 is a wasteful number, since it uses less digits than its factorization.

21555983 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1268016.

The product of its digits is 54000, while the sum is 38.

The square root of 21555983 is about 4642.8421252504. The cubic root of 21555983 is about 278.3060265401.

The spelling of 21555983 in words is "twenty-one million, five hundred fifty-five thousand, nine hundred eighty-three".