21646945 has 4 divisors (see below), whose sum is σ = 25976340. Its totient is φ = 17317552.

The previous prime is 21646943. The next prime is 21646973. The reversal of 21646945 is 54964612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9585216 + 12061729 = 3096^2 + 3473^2 .

It is a cyclic number.

It is not a de Polignac number, because 21646945 - 2¹ = 21646943 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21646943) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2164690 + ... + 2164699.

It is an arithmetic number, because the mean of its divisors is an integer number (6494085).

Almost surely, 2^21646945 is an apocalyptic number.

It is an amenable number.

21646945 is a deficient number, since it is larger than the sum of its proper divisors (4329395).

21646945 is an equidigital number, since it uses as much as digits as its factorization.

21646945 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4329394.

The product of its digits is 51840, while the sum is 37.

The square root of 21646945 is about 4652.6277521418. The cubic root of 21646945 is about 278.6969427193.

The spelling of 21646945 in words is "twenty-one million, six hundred forty-six thousand, nine hundred forty-five".