21279978 has 24 divisors (see below), whose sum is σ = 46758816. Its totient is φ = 6993000.

The previous prime is 21279959. The next prime is 21280001. The reversal of 21279978 is 87997212.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 7048 + ... + 9603.

It is an arithmetic number, because the mean of its divisors is an integer number (1948284).

Almost surely, 2^21279978 is an apocalyptic number.

21279978 is an abundant number, since it is smaller than the sum of its proper divisors (25478838).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21279978 is a wasteful number, since it uses less digits than its factorization.

21279978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16730 (or 16727 counting only the distinct ones).

The product of its digits is 127008, while the sum is 45.

The square root of 21279978 is about 4613.0226533153. The cubic root of 21279978 is about 277.1131009507.

The spelling of 21279978 in words is "twenty-one million, two hundred seventy-nine thousand, nine hundred seventy-eight".