21645817 has 2 divisors, whose sum is σ = 21645818. Its totient is φ = 21645816.

The previous prime is 21645809. The next prime is 21645859. The reversal of 21645817 is 71854612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11634921 + 10010896 = 3411^2 + 3164^2 .

It is a cyclic number.

It is not a de Polignac number, because 21645817 - 2³ = 21645809 is a prime.

It is not a weakly prime, because it can be changed into another prime (21645317) 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, 10822908 + 10822909.

It is an arithmetic number, because the mean of its divisors is an integer number (10822909).

Almost surely, 2^21645817 is an apocalyptic number.

It is an amenable number.

21645817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21645817 is an equidigital number, since it uses as much as digits as its factorization.

21645817 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 13440, while the sum is 34.

The square root of 21645817 is about 4652.5065287434. The cubic root of 21645817 is about 278.6921017651.

The spelling of 21645817 in words is "twenty-one million, six hundred forty-five thousand, eight hundred seventeen".