21281278 has 4 divisors (see below), whose sum is σ = 31921920. Its totient is φ = 10640638.

The previous prime is 21281261. The next prime is 21281321. The reversal of 21281278 is 87218212.

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

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5320318 + ... + 5320321.

It is an arithmetic number, because the mean of its divisors is an integer number (7980480).

Almost surely, 2^21281278 is an apocalyptic number.

21281278 is a deficient number, since it is larger than the sum of its proper divisors (10640642).

21281278 is a wasteful number, since it uses less digits than its factorization.

21281278 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10640641.

The product of its digits is 3584, while the sum is 31.

The square root of 21281278 is about 4613.1635566062. The cubic root of 21281278 is about 277.1187438089.

The spelling of 21281278 in words is "twenty-one million, two hundred eighty-one thousand, two hundred seventy-eight".