21685287 has 32 divisors (see below), whose sum is σ = 32505088. Its totient is φ = 12773376.

The previous prime is 21685277. The next prime is 21685309. The reversal of 21685287 is 78258612.

It is not a de Polignac number, because 21685287 - 2⁴ = 21685271 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21685207) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 112263 + ... + 112455.

It is an arithmetic number, because the mean of its divisors is an integer number (1015784).

Almost surely, 2^21685287 is an apocalyptic number.

21685287 is a deficient number, since it is larger than the sum of its proper divisors (10819801).

21685287 is a wasteful number, since it uses less digits than its factorization.

21685287 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 319.

The product of its digits is 53760, while the sum is 39.

The square root of 21685287 is about 4656.7463963587. The cubic root of 21685287 is about 278.8613923346.

The spelling of 21685287 in words is "twenty-one million, six hundred eighty-five thousand, two hundred eighty-seven".