21778149 has 16 divisors (see below), whose sum is σ = 29801408. Its totient is φ = 14141952.

The previous prime is 21778117. The next prime is 21778157. The reversal of 21778149 is 94187712.

It is not a de Polignac number, because 21778149 - 2⁵ = 21778117 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21778109) 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 15 ways as a sum of consecutive naturals, for example, 18939 + ... + 20055.

It is an arithmetic number, because the mean of its divisors is an integer number (1862588).

Almost surely, 2^21778149 is an apocalyptic number.

It is an amenable number.

21778149 is a deficient number, since it is larger than the sum of its proper divisors (8023259).

21778149 is a wasteful number, since it uses less digits than its factorization.

21778149 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1284.

The product of its digits is 28224, while the sum is 39.

The square root of 21778149 is about 4666.7064403067. The cubic root of 21778149 is about 279.2588776646.

The spelling of 21778149 in words is "twenty-one million, seven hundred seventy-eight thousand, one hundred forty-nine".