21686865 has 16 divisors (see below), whose sum is σ = 34758528. Its totient is φ = 11546496.

The previous prime is 21686851. The next prime is 21686869. The reversal of 21686865 is 56868612.

It is not a de Polignac number, because 21686865 - 2¹⁶ = 21621329 is a prime.

It is a super-2 number, since 2×21686865² = 940640227056450, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21686869) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13284 + ... + 14826.

It is an arithmetic number, because the mean of its divisors is an integer number (2172408).

Almost surely, 2^21686865 is an apocalyptic number.

It is an amenable number.

21686865 is a deficient number, since it is larger than the sum of its proper divisors (13071663).

21686865 is a wasteful number, since it uses less digits than its factorization.

21686865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2488.

The product of its digits is 138240, while the sum is 42.

The square root of 21686865 is about 4656.9158248781. The cubic root of 21686865 is about 278.8681562540.

The spelling of 21686865 in words is "twenty-one million, six hundred eighty-six thousand, eight hundred sixty-five".