21738561 has 16 divisors (see below), whose sum is σ = 31382400. Its totient is φ = 13305600.

The previous prime is 21738551. The next prime is 21738571. The reversal of 21738561 is 16583712.

It is an interprime number because it is at equal distance from previous prime (21738551) and next prime (21738571).

It is not a de Polignac number, because 21738561 - 2⁹ = 21738049 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21738551) 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 15 ways as a sum of consecutive naturals, for example, 6361 + ... + 9161.

It is an arithmetic number, because the mean of its divisors is an integer number (1961400).

Almost surely, 2^21738561 is an apocalyptic number.

It is an amenable number.

21738561 is a deficient number, since it is larger than the sum of its proper divisors (9643839).

21738561 is a wasteful number, since it uses less digits than its factorization.

21738561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3016.

The product of its digits is 10080, while the sum is 33.

The square root of 21738561 is about 4662.4629757243. The cubic root of 21738561 is about 279.0895641333.

The spelling of 21738561 in words is "twenty-one million, seven hundred thirty-eight thousand, five hundred sixty-one".