21378455 has 24 divisors (see below), whose sum is σ = 30287520. Its totient is φ = 14441280.

The previous prime is 21378443. The next prime is 21378457. The reversal of 21378455 is 55487312.

It is a happy number.

It is not a de Polignac number, because 21378455 - 2²⁰ = 20329879 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (35).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21378457) 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 23 ways as a sum of consecutive naturals, for example, 16781 + ... + 18009.

It is an arithmetic number, because the mean of its divisors is an integer number (1261980).

Almost surely, 2^21378455 is an apocalyptic number.

21378455 is a deficient number, since it is larger than the sum of its proper divisors (8909065).

21378455 is a wasteful number, since it uses less digits than its factorization.

21378455 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1319 (or 1312 counting only the distinct ones).

The product of its digits is 33600, while the sum is 35.

The square root of 21378455 is about 4623.6841371357. The cubic root of 21378455 is about 277.5399071466.

The spelling of 21378455 in words is "twenty-one million, three hundred seventy-eight thousand, four hundred fifty-five".