21257756 has 12 divisors (see below), whose sum is σ = 40062792. Its totient is φ = 9811248.

The previous prime is 21257749. The next prime is 21257767. The reversal of 21257756 is 65775212.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 204350 + ... + 204453.

It is an arithmetic number, because the mean of its divisors is an integer number (3338566).

Almost surely, 2^21257756 is an apocalyptic number.

21257756 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

21257756 is a deficient number, since it is larger than the sum of its proper divisors (18805036).

21257756 is a wasteful number, since it uses less digits than its factorization.

21257756 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 408820 (or 408818 counting only the distinct ones).

The product of its digits is 29400, while the sum is 35.

The square root of 21257756 is about 4610.6134082137. The cubic root of 21257756 is about 277.0166072402.

The spelling of 21257756 in words is "twenty-one million, two hundred fifty-seven thousand, seven hundred fifty-six".