21217844 has 6 divisors (see below), whose sum is σ = 37131234. Its totient is φ = 10608920.

The previous prime is 21217837. The next prime is 21217849. The reversal of 21217844 is 44871212.

It can be written as a sum of positive squares in only one way, i.e., 21049744 + 168100 = 4588^2 + 410^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21217849) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2652227 + ... + 2652234.

It is an arithmetic number, because the mean of its divisors is an integer number (6188539).

Almost surely, 2^21217844 is an apocalyptic number.

It is an amenable number.

21217844 is a deficient number, since it is larger than the sum of its proper divisors (15913390).

21217844 is a wasteful number, since it uses less digits than its factorization.

21217844 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5304465 (or 5304463 counting only the distinct ones).

The product of its digits is 3584, while the sum is 29.

The square root of 21217844 is about 4606.2831002881. The cubic root of 21217844 is about 276.8431299528.

The spelling of 21217844 in words is "twenty-one million, two hundred seventeen thousand, eight hundred forty-four".