21564361 has 24 divisors (see below), whose sum is σ = 27371400. Its totient is φ = 16837632.

The previous prime is 21564353. The next prime is 21564379. The reversal of 21564361 is 16346512.

It can be written as a sum of positive squares in 4 ways, for example, as 1806336 + 19758025 = 1344^2 + 4445^2 .

It is not a de Polignac number, because 21564361 - 2³ = 21564353 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21564311) 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 23 ways as a sum of consecutive naturals, for example, 61615 + ... + 61963.

It is an arithmetic number, because the mean of its divisors is an integer number (1140475).

Almost surely, 2^21564361 is an apocalyptic number.

It is an amenable number.

21564361 is a deficient number, since it is larger than the sum of its proper divisors (5807039).

21564361 is a wasteful number, since it uses less digits than its factorization.

21564361 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 473 (or 466 counting only the distinct ones).

The product of its digits is 4320, while the sum is 28.

The square root of 21564361 is about 4643.7442866721. The cubic root of 21564361 is about 278.3420775656.

The spelling of 21564361 in words is "twenty-one million, five hundred sixty-four thousand, three hundred sixty-one".