21305040 has 40 divisors (see below), whose sum is σ = 66046368. Its totient is φ = 5681280.

The previous prime is 21305027. The next prime is 21305047. The reversal of 21305040 is 4050312.

It is a tau number, because it is divible by the number of its divisors (40).

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21305047) 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, 44146 + ... + 44625.

Almost surely, 2^21305040 is an apocalyptic number.

21305040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21305040 is an abundant number, since it is smaller than the sum of its proper divisors (44741328).

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

21305040 is a wasteful number, since it uses less digits than its factorization.

21305040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 88787 (or 88781 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 15.

The square root of 21305040 is about 4615.7382941410. The cubic root of 21305040 is about 277.2218461114.

Adding to 21305040 its reverse (4050312), we get a palindrome (25355352).

The spelling of 21305040 in words is "twenty-one million, three hundred five thousand, forty".