21311978 has 8 divisors (see below), whose sum is σ = 31989540. Its totient is φ = 10648800.

The previous prime is 21311959. The next prime is 21311981. The reversal of 21311978 is 87911312.

It can be written as a sum of positive squares in 2 ways, for example, as 20729809 + 582169 = 4553^2 + 763^2 .

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

It is a Curzon number.

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, 1628 + ... + 6728.

Almost surely, 2^21311978 is an apocalyptic number.

21311978 is a deficient number, since it is larger than the sum of its proper divisors (10677562).

21311978 is a wasteful number, since it uses less digits than its factorization.

21311978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7192.

The product of its digits is 3024, while the sum is 32.

The square root of 21311978 is about 4616.4897920390. The cubic root of 21311978 is about 277.2519353363.

The spelling of 21311978 in words is "twenty-one million, three hundred eleven thousand, nine hundred seventy-eight".