21213444 has 24 divisors (see below), whose sum is σ = 56569408. Its totient is φ = 6060960.

The previous prime is 21213431. The next prime is 21213449. The reversal of 21213444 is 44431212.

It is a super-2 number, since 2×21213444² = 900020412682272, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a nude number because it is divisible by every one of its digits.

It is a self number, because there is not a number n which added to its sum of digits gives 21213444.

It is not an unprimeable number, because it can be changed into a prime (21213449) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 126187 + ... + 126354.

Almost surely, 2^21213444 is an apocalyptic number.

It is an amenable number.

21213444 is an abundant number, since it is smaller than the sum of its proper divisors (35355964).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21213444 is a wasteful number, since it uses less digits than its factorization.

21213444 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 252555 (or 252553 counting only the distinct ones).

The product of its digits is 768, while the sum is 21.

The square root of 21213444 is about 4605.8054670166. The cubic root of 21213444 is about 276.8239920677.

Adding to 21213444 its reverse (44431212), we get a palindrome (65644656).

It can be divided in two parts, 2121 and 3444, that added together give a triangular number (5565 = T₁₀₅).

The spelling of 21213444 in words is "twenty-one million, two hundred thirteen thousand, four hundred forty-four".