21378433 has 4 divisors (see below), whose sum is σ = 21413700. Its totient is φ = 21343168.

The previous prime is 21378421. The next prime is 21378443. The reversal of 21378433 is 33487312.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1912689 + 19465744 = 1383^2 + 4412^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21378433 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21378395 and 21378404.

It is not an unprimeable number, because it can be changed into a prime (21378443) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16708 + ... + 17941.

It is an arithmetic number, because the mean of its divisors is an integer number (5353425).

Almost surely, 2^21378433 is an apocalyptic number.

It is an amenable number.

21378433 is a deficient number, since it is larger than the sum of its proper divisors (35267).

21378433 is an equidigital number, since it uses as much as digits as its factorization.

21378433 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35266.

The product of its digits is 12096, while the sum is 31.

The square root of 21378433 is about 4623.6817580798. The cubic root of 21378433 is about 277.5398119435.

The spelling of 21378433 in words is "twenty-one million, three hundred seventy-eight thousand, four hundred thirty-three".