21685745 has 32 divisors (see below), whose sum is σ = 28771200. Its totient is φ = 15634944.

The previous prime is 21685739. The next prime is 21685751. The reversal of 21685745 is 54758612.

It is an interprime number because it is at equal distance from previous prime (21685739) and next prime (21685751).

It is a cyclic number.

It is not a de Polignac number, because 21685745 - 2¹⁸ = 21423601 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21685699 and 21685708.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 297029 + ... + 297101.

It is an arithmetic number, because the mean of its divisors is an integer number (899100).

Almost surely, 2^21685745 is an apocalyptic number.

It is an amenable number.

21685745 is a deficient number, since it is larger than the sum of its proper divisors (7085455).

21685745 is a wasteful number, since it uses less digits than its factorization.

21685745 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 209.

The product of its digits is 67200, while the sum is 38.

The square root of 21685745 is about 4656.7955720646. The cubic root of 21685745 is about 278.8633555338.

The spelling of 21685745 in words is "twenty-one million, six hundred eighty-five thousand, seven hundred forty-five".