21706978 has 8 divisors (see below), whose sum is σ = 32645340. Its totient is φ = 10825200.

The previous prime is 21706939. The next prime is 21706981. The reversal of 21706978 is 87960712.

It can be written as a sum of positive squares in 2 ways, for example, as 21501769 + 205209 = 4637^2 + 453^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21706978.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13173 + ... + 14728.

Almost surely, 2^21706978 is an apocalyptic number.

21706978 is a deficient number, since it is larger than the sum of its proper divisors (10938362).

21706978 is a wasteful number, since it uses less digits than its factorization.

21706978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28292.

The product of its (nonzero) digits is 42336, while the sum is 40.

The square root of 21706978 is about 4659.0748008591. The cubic root of 21706978 is about 278.9543396370.

The spelling of 21706978 in words is "twenty-one million, seven hundred six thousand, nine hundred seventy-eight".