21278986 has 4 divisors (see below), whose sum is σ = 31918482. Its totient is φ = 10639492.

The previous prime is 21278981. The next prime is 21279029. The reversal of 21278986 is 68987212.

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

It can be written as a sum of positive squares in only one way, i.e., 20875761 + 403225 = 4569^2 + 635^2 .

It is not an unprimeable number, because it can be changed into a prime (21278981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5319745 + ... + 5319748.

Almost surely, 2^21278986 is an apocalyptic number.

21278986 is a deficient number, since it is larger than the sum of its proper divisors (10639496).

21278986 is a wasteful number, since it uses less digits than its factorization.

21278986 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10639495.

The product of its digits is 96768, while the sum is 43.

The square root of 21278986 is about 4612.9151303704. The cubic root of 21278986 is about 277.1087948613.

The spelling of 21278986 in words is "twenty-one million, two hundred seventy-eight thousand, nine hundred eighty-six".