21278923 has 2 divisors, whose sum is σ = 21278924. Its totient is φ = 21278922.

The previous prime is 21278911. The next prime is 21278941. The reversal of 21278923 is 32987212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21278923 - 2¹⁷ = 21147851 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (21278963) by changing a digit.

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, 10639461 + 10639462.

It is an arithmetic number, because the mean of its divisors is an integer number (10639462).

Almost surely, 2^21278923 is an apocalyptic number.

21278923 is a deficient number, since it is larger than the sum of its proper divisors (1).

21278923 is an equidigital number, since it uses as much as digits as its factorization.

21278923 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12096, while the sum is 34.

The square root of 21278923 is about 4612.9083017116. The cubic root of 21278923 is about 277.1085213853.

It can be divided in two parts, 21278 and 923, that added together give a square (22201 = 149²).

The spelling of 21278923 in words is "twenty-one million, two hundred seventy-eight thousand, nine hundred twenty-three".