21278771 has 4 divisors (see below), whose sum is σ = 21578544. Its totient is φ = 20979000.

The previous prime is 21278711. The next prime is 21278773. The reversal of 21278771 is 17787212.

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

It is a cyclic number.

It is not a de Polignac number, because 21278771 - 2¹⁰ = 21277747 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21278773) 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, 149780 + ... + 149921.

It is an arithmetic number, because the mean of its divisors is an integer number (5394636).

Almost surely, 2^21278771 is an apocalyptic number.

21278771 is a deficient number, since it is larger than the sum of its proper divisors (299773).

21278771 is an equidigital number, since it uses as much as digits as its factorization.

21278771 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 299772.

The product of its digits is 10976, while the sum is 35.

The square root of 21278771 is about 4612.8918261759. The cubic root of 21278771 is about 277.1078615682.

The spelling of 21278771 in words is "twenty-one million, two hundred seventy-eight thousand, seven hundred seventy-one".