21685761 has 24 divisors (see below), whose sum is σ = 33985224. Its totient is φ = 13271040.

The previous prime is 21685751. The next prime is 21685787. The reversal of 21685761 is 16758612.

21685761 is a `hidden beast` number, since 21 + 68 + 576 + 1 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 119025 + 21566736 = 345^2 + 4644^2 .

It is not a de Polignac number, because 21685761 - 2⁹ = 21685249 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21685721) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4545 + ... + 8001.

It is an arithmetic number, because the mean of its divisors is an integer number (1416051).

Almost surely, 2^21685761 is an apocalyptic number.

It is an amenable number.

21685761 is a deficient number, since it is larger than the sum of its proper divisors (12299463).

21685761 is a wasteful number, since it uses less digits than its factorization.

21685761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3521 (or 3518 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

The square root of 21685761 is about 4656.7972899838. The cubic root of 21685761 is about 278.8634241167.

The spelling of 21685761 in words is "twenty-one million, six hundred eighty-five thousand, seven hundred sixty-one".