21257788 has 6 divisors (see below), whose sum is σ = 37201136. Its totient is φ = 10628892.

The previous prime is 21257779. The next prime is 21257791. The reversal of 21257788 is 88775212.

It is a self number, because there is not a number n which added to its sum of digits gives 21257788.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2657220 + ... + 2657227.

Almost surely, 2^21257788 is an apocalyptic number.

It is an amenable number.

21257788 is a deficient number, since it is larger than the sum of its proper divisors (15943348).

21257788 is a wasteful number, since it uses less digits than its factorization.

21257788 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5314451 (or 5314449 counting only the distinct ones).

The product of its digits is 62720, while the sum is 40.

The square root of 21257788 is about 4610.6168784665. The cubic root of 21257788 is about 277.0167462409.

The spelling of 21257788 in words is "twenty-one million, two hundred fifty-seven thousand, seven hundred eighty-eight".