21257766 has 12 divisors (see below), whose sum is σ = 46058532. Its totient is φ = 7085916.

The previous prime is 21257749. The next prime is 21257767. The reversal of 21257766 is 66775212.

21257766 is a `hidden beast` number, since 21 + 2 + 577 + 66 = 666.

It is a self number, because there is not a number n which added to its sum of digits gives 21257766.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21257767) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 590476 + ... + 590511.

It is an arithmetic number, because the mean of its divisors is an integer number (3838211).

Almost surely, 2^21257766 is an apocalyptic number.

21257766 is an abundant number, since it is smaller than the sum of its proper divisors (24800766).

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

21257766 is a wasteful number, since it uses less digits than its factorization.

21257766 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1180995 (or 1180992 counting only the distinct ones).

The product of its digits is 35280, while the sum is 36.

The square root of 21257766 is about 4610.6144926680. The cubic root of 21257766 is about 277.0166506779.

The spelling of 21257766 in words is "twenty-one million, two hundred fifty-seven thousand, seven hundred sixty-six".