21242340 has 144 divisors (see below), whose sum is σ = 76946688. Its totient is φ = 4637952.

The previous prime is 21242339. The next prime is 21242357. The reversal of 21242340 is 4324212.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 28614 + ... + 29346.

It is an arithmetic number, because the mean of its divisors is an integer number (534352).

Almost surely, 2^21242340 is an apocalyptic number.

21242340 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 21242340, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38473344).

21242340 is an abundant number, since it is smaller than the sum of its proper divisors (55704348).

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

21242340 is a wasteful number, since it uses less digits than its factorization.

21242340 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 778 (or 773 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 18.

The square root of 21242340 is about 4608.9413101058. The cubic root of 21242340 is about 276.9496274401.

Adding to 21242340 its reverse (4324212), we get a palindrome (25566552).

The spelling of 21242340 in words is "twenty-one million, two hundred forty-two thousand, three hundred forty".