21680817 has 4 divisors (see below), whose sum is σ = 28907760. Its totient is φ = 14453876.

The previous prime is 21680807. The next prime is 21680819. The reversal of 21680817 is 71808612.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21680817 - 2⁴ = 21680801 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21680819) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3613467 + ... + 3613472.

It is an arithmetic number, because the mean of its divisors is an integer number (7226940).

Almost surely, 2^21680817 is an apocalyptic number.

It is an amenable number.

21680817 is a deficient number, since it is larger than the sum of its proper divisors (7226943).

21680817 is an equidigital number, since it uses as much as digits as its factorization.

21680817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7226942.

The product of its (nonzero) digits is 5376, while the sum is 33.

The square root of 21680817 is about 4656.2664227898. The cubic root of 21680817 is about 278.8422304011.

The spelling of 21680817 in words is "twenty-one million, six hundred eighty thousand, eight hundred seventeen".