21405140 has 12 divisors (see below), whose sum is σ = 44950836. Its totient is φ = 8562048.

The previous prime is 21405127. The next prime is 21405149. The reversal of 21405140 is 4150412.

It can be written as a sum of positive squares in 2 ways, for example, as 5373124 + 16032016 = 2318^2 + 4004^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21405149) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 535109 + ... + 535148.

It is an arithmetic number, because the mean of its divisors is an integer number (3745903).

Almost surely, 2^21405140 is an apocalyptic number.

21405140 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21405140 is an abundant number, since it is smaller than the sum of its proper divisors (23545696).

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

21405140 is a wasteful number, since it uses less digits than its factorization.

21405140 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1070266 (or 1070264 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 17.

The square root of 21405140 is about 4626.5689230790. The cubic root of 21405140 is about 277.6553360220.

Adding to 21405140 its reverse (4150412), we get a palindrome (25555552).

The spelling of 21405140 in words is "twenty-one million, four hundred five thousand, one hundred forty".