21755987 has 4 divisors (see below), whose sum is σ = 23733816. Its totient is φ = 19778160.

The previous prime is 21755959. The next prime is 21756041. The reversal of 21755987 is 78955712.

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 21755987 - 2¹⁴ = 21739603 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21745987) 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, 988898 + ... + 988919.

It is an arithmetic number, because the mean of its divisors is an integer number (5933454).

Almost surely, 2^21755987 is an apocalyptic number.

21755987 is a deficient number, since it is larger than the sum of its proper divisors (1977829).

21755987 is a wasteful number, since it uses less digits than its factorization.

21755987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1977828.

The product of its digits is 176400, while the sum is 44.

The square root of 21755987 is about 4664.3313561538. The cubic root of 21755987 is about 279.1641185283.

The spelling of 21755987 in words is "twenty-one million, seven hundred fifty-five thousand, nine hundred eighty-seven".