21005766 has 12 divisors (see below), whose sum is σ = 45512532. Its totient is φ = 7001916.

The previous prime is 21005759. The next prime is 21005767. The reversal of 21005766 is 66750012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005767) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 583476 + ... + 583511.

It is an arithmetic number, because the mean of its divisors is an integer number (3792711).

Almost surely, 2^21005766 is an apocalyptic number.

21005766 is an abundant number, since it is smaller than the sum of its proper divisors (24506766).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21005766 is a wasteful number, since it uses less digits than its factorization.

21005766 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1166995 (or 1166992 counting only the distinct ones).

The product of its (nonzero) digits is 2520, while the sum is 27.

The square root of 21005766 is about 4583.2047739546. The cubic root of 21005766 is about 275.9176660525.

Adding to 21005766 its reverse (66750012), we get a palindrome (87755778).

The spelling of 21005766 in words is "twenty-one million, five thousand, seven hundred sixty-six".