21278399 has 2 divisors, whose sum is σ = 21278400. Its totient is φ = 21278398.

The previous prime is 21278393. The next prime is 21278401. The reversal of 21278399 is 99387212.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21278399 is a prime.

Together with 21278401, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21278393) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10639199 + 10639200.

It is an arithmetic number, because the mean of its divisors is an integer number (10639200).

Almost surely, 2^21278399 is an apocalyptic number.

21278399 is a deficient number, since it is larger than the sum of its proper divisors (1).

21278399 is an equidigital number, since it uses as much as digits as its factorization.

21278399 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 54432, while the sum is 41.

The square root of 21278399 is about 4612.8515042217. The cubic root of 21278399 is about 277.1062467392.

The spelling of 21278399 in words is "twenty-one million, two hundred seventy-eight thousand, three hundred ninety-nine".