21305340 has 144 divisors (see below), whose sum is σ = 76020672. Its totient is φ = 4727808.

The previous prime is 21305321. The next prime is 21305341. The reversal of 21305340 is 4350312.

21305340 is a `hidden beast` number, since 2 + 130 + 534 + 0 = 666.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21305341) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 46392 + ... + 46848.

Almost surely, 2^21305340 is an apocalyptic number.

21305340 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 21305340, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38010336).

21305340 is an abundant number, since it is smaller than the sum of its proper divisors (54715332).

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

21305340 is a wasteful number, since it uses less digits than its factorization.

21305340 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 516 (or 511 counting only the distinct ones).

The product of its (nonzero) digits is 360, while the sum is 18.

The square root of 21305340 is about 4615.7707915363. The cubic root of 21305340 is about 277.2231473084.

Adding to 21305340 its reverse (4350312), we get a palindrome (25655652).

The spelling of 21305340 in words is "twenty-one million, three hundred five thousand, three hundred forty".