21443440 has 20 divisors (see below), whose sum is σ = 49856184. Its totient is φ = 8577344.

The previous prime is 21443437. The next prime is 21443447. The reversal of 21443440 is 4434412.

It is a tau number, because it is divible by the number of its divisors (20).

It is a super-2 number, since 2×21443440² = 919642238067200, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21443447) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 133942 + ... + 134101.

Almost surely, 2^21443440 is an apocalyptic number.

21443440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21443440 is an abundant number, since it is smaller than the sum of its proper divisors (28412744).

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

21443440 is a wasteful number, since it uses less digits than its factorization.

21443440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 268056 (or 268050 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 22.

The square root of 21443440 is about 4630.7062096402. The cubic root of 21443440 is about 277.8208393094.

Adding to 21443440 its reverse (4434412), we get a palindrome (25877852).

Subtracting from 21443440 its reverse (4434412), we obtain a triangular number (17009028 = T₅₈₃₂).

The spelling of 21443440 in words is "twenty-one million, four hundred forty-three thousand, four hundred forty".