21081766 has 4 divisors (see below), whose sum is σ = 31622652. Its totient is φ = 10540882.

The previous prime is 21081763. The next prime is 21081787. The reversal of 21081766 is 66718012.

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

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21081761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5270440 + ... + 5270443.

It is an arithmetic number, because the mean of its divisors is an integer number (7905663).

Almost surely, 2^21081766 is an apocalyptic number.

21081766 is a deficient number, since it is larger than the sum of its proper divisors (10540886).

21081766 is a wasteful number, since it uses less digits than its factorization.

21081766 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10540885.

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 21081766 is about 4591.4884296925. The cubic root of 21081766 is about 276.2500272312.

Adding to 21081766 its reverse (66718012), we get a palindrome (87799778).

The spelling of 21081766 in words is "twenty-one million, eighty-one thousand, seven hundred sixty-six".