21644461 has 2 divisors, whose sum is σ = 21644462. Its totient is φ = 21644460.

The previous prime is 21644459. The next prime is 21644471. The reversal of 21644461 is 16444612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12823561 + 8820900 = 3581^2 + 2970^2 .

It is a cyclic number.

It is not a de Polignac number, because 21644461 - 2¹ = 21644459 is a prime.

Together with 21644459, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21644471) 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 as a sum of consecutive naturals, namely, 10822230 + 10822231.

It is an arithmetic number, because the mean of its divisors is an integer number (10822231).

Almost surely, 2^21644461 is an apocalyptic number.

It is an amenable number.

21644461 is a deficient number, since it is larger than the sum of its proper divisors (1).

21644461 is an equidigital number, since it uses as much as digits as its factorization.

21644461 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4608, while the sum is 28.

The square root of 21644461 is about 4652.3607985624. The cubic root of 21644461 is about 278.6862820974.

The spelling of 21644461 in words is "twenty-one million, six hundred forty-four thousand, four hundred sixty-one".