21405878 has 12 divisors (see below), whose sum is σ = 34769268. Its totient is φ = 9879480.

The previous prime is 21405877. The next prime is 21405887. The reversal of 21405878 is 87850412.

It is a super-2 number, since 2×21405878² = 916423225901768, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21405871) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 31328 + ... + 32003.

It is an arithmetic number, because the mean of its divisors is an integer number (2897439).

Almost surely, 2^21405878 is an apocalyptic number.

21405878 is a deficient number, since it is larger than the sum of its proper divisors (13363390).

21405878 is a wasteful number, since it uses less digits than its factorization.

21405878 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 63359 (or 63346 counting only the distinct ones).

The product of its (nonzero) digits is 17920, while the sum is 35.

The square root of 21405878 is about 4626.6486791197. The cubic root of 21405878 is about 277.6585269578.

The spelling of 21405878 in words is "twenty-one million, four hundred five thousand, eight hundred seventy-eight".