21278567 has 2 divisors, whose sum is σ = 21278568. Its totient is φ = 21278566.

The previous prime is 21278557. The next prime is 21278573. The reversal of 21278567 is 76587212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21278567 - 2⁸ = 21278311 is a prime.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21278567.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21278557) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10639283 + 10639284.

It is an arithmetic number, because the mean of its divisors is an integer number (10639284).

Almost surely, 2^21278567 is an apocalyptic number.

21278567 is a deficient number, since it is larger than the sum of its proper divisors (1).

21278567 is an equidigital number, since it uses as much as digits as its factorization.

21278567 is an evil number, because the sum of its binary digits is even.

The product of its digits is 47040, while the sum is 38.

The square root of 21278567 is about 4612.8697141801. The cubic root of 21278567 is about 277.1069760192.

The spelling of 21278567 in words is "twenty-one million, two hundred seventy-eight thousand, five hundred sixty-seven".