21434240 has 64 divisors (see below), whose sum is σ = 51885360. Its totient is φ = 8466432.

The previous prime is 21434233. The next prime is 21434249. The reversal of 21434240 is 4243412.

It is a tau number, because it is divible by the number of its divisors (64).

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21434249) 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, 68324 + ... + 68636.

Almost surely, 2^21434240 is an apocalyptic number.

21434240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21434240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25942680).

21434240 is an abundant number, since it is smaller than the sum of its proper divisors (30451120).

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

21434240 is a wasteful number, since it uses less digits than its factorization.

21434240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 439 (or 427 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 20.

The square root of 21434240 is about 4629.7127340689. The cubic root of 21434240 is about 277.7811019454.

Adding to 21434240 its reverse (4243412), we get a palindrome (25677652).

The spelling of 21434240 in words is "twenty-one million, four hundred thirty-four thousand, two hundred forty".