21405040 has 40 divisors (see below), whose sum is σ = 52697520. Its totient is φ = 8057856.

The previous prime is 21404983. The next prime is 21405047. The reversal of 21405040 is 4050412.

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 (16).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21405047) 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, 6510 + ... + 9229.

It is an arithmetic number, because the mean of its divisors is an integer number (1317438).

Almost surely, 2^21405040 is an apocalyptic number.

21405040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21405040 is an abundant number, since it is smaller than the sum of its proper divisors (31292480).

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

21405040 is a wasteful number, since it uses less digits than its factorization.

21405040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15769 (or 15763 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 16.

The square root of 21405040 is about 4626.5581159216. The cubic root of 21405040 is about 277.6549036402.

Adding to 21405040 its reverse (4050412), we get a palindrome (25455452).

The spelling of 21405040 in words is "twenty-one million, four hundred five thousand, forty".