21685556 has 12 divisors (see below), whose sum is σ = 38875620. Its totient is φ = 10578240.

The previous prime is 21685553. The next prime is 21685571. The reversal of 21685556 is 65558612.

It can be written as a sum of positive squares in 2 ways, for example, as 2149156 + 19536400 = 1466^2 + 4420^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21685553) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 65951 + ... + 66278.

It is an arithmetic number, because the mean of its divisors is an integer number (3239635).

Almost surely, 2^21685556 is an apocalyptic number.

It is an amenable number.

21685556 is a deficient number, since it is larger than the sum of its proper divisors (17190064).

21685556 is a wasteful number, since it uses less digits than its factorization.

21685556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132274 (or 132272 counting only the distinct ones).

The product of its digits is 72000, while the sum is 38.

The square root of 21685556 is about 4656.7752790960. The cubic root of 21685556 is about 278.8625453960.

The spelling of 21685556 in words is "twenty-one million, six hundred eighty-five thousand, five hundred fifty-six".