21858644 has 6 divisors (see below), whose sum is σ = 38252634. Its totient is φ = 10929320.

The previous prime is 21858643. The next prime is 21858647. The reversal of 21858644 is 44685812.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 14899600 + 6959044 = 3860^2 + 2638^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21858598 and 21858607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21858643) 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, 2732327 + ... + 2732334.

It is an arithmetic number, because the mean of its divisors is an integer number (6375439).

Almost surely, 2^21858644 is an apocalyptic number.

It is an amenable number.

21858644 is a deficient number, since it is larger than the sum of its proper divisors (16393990).

21858644 is a wasteful number, since it uses less digits than its factorization.

21858644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5464665 (or 5464663 counting only the distinct ones).

The product of its digits is 61440, while the sum is 38.

The square root of 21858644 is about 4675.3228765509. The cubic root of 21858644 is about 279.6025142307.

The spelling of 21858644 in words is "twenty-one million, eight hundred fifty-eight thousand, six hundred forty-four".