21297778 has 16 divisors (see below), whose sum is σ = 32931360. Its totient is φ = 10324000.

The previous prime is 21297767. The next prime is 21297779. The reversal of 21297778 is 87779212.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21297779) 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 7 ways as a sum of consecutive naturals, for example, 13953 + ... + 15403.

It is an arithmetic number, because the mean of its divisors is an integer number (2058210).

Almost surely, 2^21297778 is an apocalyptic number.

21297778 is a deficient number, since it is larger than the sum of its proper divisors (11633582).

21297778 is a wasteful number, since it uses less digits than its factorization.

21297778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1673.

The product of its digits is 98784, while the sum is 43.

The square root of 21297778 is about 4614.9515707101. The cubic root of 21297778 is about 277.1903447416.

The spelling of 21297778 in words is "twenty-one million, two hundred ninety-seven thousand, seven hundred seventy-eight".