21791978 has 8 divisors (see below), whose sum is σ = 35202468. Its totient is φ = 10057824.

The previous prime is 21791969. The next prime is 21791983. The reversal of 21791978 is 87919712.

It can be written as a sum of positive squares in 2 ways, for example, as 21687649 + 104329 = 4657^2 + 323^2 .

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

It is a Curzon number.

It is a plaindrome in base 11.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 419051 + ... + 419102.

Almost surely, 2^21791978 is an apocalyptic number.

21791978 is a deficient number, since it is larger than the sum of its proper divisors (13410490).

21791978 is a wasteful number, since it uses less digits than its factorization.

21791978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 838168.

The product of its digits is 63504, while the sum is 44.

The square root of 21791978 is about 4668.1878711123. The cubic root of 21791978 is about 279.3179744208.

The spelling of 21791978 in words is "twenty-one million, seven hundred ninety-one thousand, nine hundred seventy-eight".