21878018 has 4 divisors (see below), whose sum is σ = 32817030. Its totient is φ = 10939008.

The previous prime is 21877951. The next prime is 21878047. The reversal of 21878018 is 81087812.

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

It can be written as a sum of positive squares in only one way, i.e., 14386849 + 7491169 = 3793^2 + 2737^2 .

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 5469503 + ... + 5469506.

Almost surely, 2^21878018 is an apocalyptic number.

21878018 is a deficient number, since it is larger than the sum of its proper divisors (10939012).

21878018 is a wasteful number, since it uses less digits than its factorization.

21878018 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10939011.

The product of its (nonzero) digits is 7168, while the sum is 35.

The square root of 21878018 is about 4677.3943601112. The cubic root of 21878018 is about 279.6850966555.

The spelling of 21878018 in words is "twenty-one million, eight hundred seventy-eight thousand, eighteen".