21806217 has 12 divisors (see below), whose sum is σ = 31649904. Its totient is φ = 14467320.

The previous prime is 21806207. The next prime is 21806227. The reversal of 21806217 is 71260812.

It is an interprime number because it is at equal distance from previous prime (21806207) and next prime (21806227).

It is not a de Polignac number, because 21806217 - 2⁷ = 21806089 is a prime.

It is a super-2 number, since 2×21806217² = 951022199702178, which contains 22 as substring.

It is a Smith number, since the sum of its digits (27) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21806207) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3843 + ... + 7640.

It is an arithmetic number, because the mean of its divisors is an integer number (2637492).

Almost surely, 2^21806217 is an apocalyptic number.

It is an amenable number.

21806217 is a deficient number, since it is larger than the sum of its proper divisors (9843687).

21806217 is a wasteful number, since it uses less digits than its factorization.

21806217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11700 (or 11697 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21806217 is about 4669.7127320639. The cubic root of 21806217 is about 279.3787971497.

The spelling of 21806217 in words is "twenty-one million, eight hundred six thousand, two hundred seventeen".