21206865 has 32 divisors (see below), whose sum is σ = 34909056. Its totient is φ = 10990080.

The previous prime is 21206849. The next prime is 21206873. The reversal of 21206865 is 56860212.

It is not a de Polignac number, because 21206865 - 2⁴ = 21206849 is a prime.

It is a super-2 number, since 2×21206865² = 899462246256450, which contains 22 as substring.

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, 117075 + ... + 117255.

It is an arithmetic number, because the mean of its divisors is an integer number (1090908).

Almost surely, 2^21206865 is an apocalyptic number.

It is an amenable number.

21206865 is a deficient number, since it is larger than the sum of its proper divisors (13702191).

21206865 is a wasteful number, since it uses less digits than its factorization.

21206865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 369.

The product of its (nonzero) digits is 5760, while the sum is 30.

The square root of 21206865 is about 4605.0912043086. The cubic root of 21206865 is about 276.7953716426.

The spelling of 21206865 in words is "twenty-one million, two hundred six thousand, eight hundred sixty-five".