21805417 has 2 divisors, whose sum is σ = 21805418. Its totient is φ = 21805416.

The previous prime is 21805411. The next prime is 21805451. The reversal of 21805417 is 71450812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21058921 + 746496 = 4589^2 + 864^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21805417 is a prime.

It is not a weakly prime, because it can be changed into another prime (21805411) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10902708 + 10902709.

It is an arithmetic number, because the mean of its divisors is an integer number (10902709).

Almost surely, 2^21805417 is an apocalyptic number.

It is an amenable number.

21805417 is a deficient number, since it is larger than the sum of its proper divisors (1).

21805417 is an equidigital number, since it uses as much as digits as its factorization.

21805417 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2240, while the sum is 28.

The square root of 21805417 is about 4669.6270729042. The cubic root of 21805417 is about 279.3753806046.

It can be divided in two parts, 21805 and 417, that added together give a palindrome (22222).

The spelling of 21805417 in words is "twenty-one million, eight hundred five thousand, four hundred seventeen".