21557866 has 16 divisors (see below), whose sum is σ = 36028800. Its totient is φ = 9590080.

The previous prime is 21557843. The next prime is 21557917. The reversal of 21557866 is 66875512.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9391 + ... + 11458.

It is an arithmetic number, because the mean of its divisors is an integer number (2251800).

Almost surely, 2^21557866 is an apocalyptic number.

21557866 is a deficient number, since it is larger than the sum of its proper divisors (14470934).

21557866 is a wasteful number, since it uses less digits than its factorization.

21557866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20909.

The product of its digits is 100800, while the sum is 40.

The square root of 21557866 is about 4643.0449060934. The cubic root of 21557866 is about 278.3141300132.

It can be divided in two parts, 215 and 57866, that added together give a square (58081 = 241²).

The spelling of 21557866 in words is "twenty-one million, five hundred fifty-seven thousand, eight hundred sixty-six".