21691778 has 16 divisors (see below), whose sum is σ = 33224256. Its totient is φ = 10619280.

The previous prime is 21691777. The next prime is 21691781. The reversal of 21691778 is 87719612.

It is not an unprimeable number, because it can be changed into a prime (21691771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 24125 + ... + 25007.

It is an arithmetic number, because the mean of its divisors is an integer number (2076516).

Almost surely, 2^21691778 is an apocalyptic number.

21691778 is a deficient number, since it is larger than the sum of its proper divisors (11532478).

21691778 is a wasteful number, since it uses less digits than its factorization.

21691778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1129.

The product of its digits is 42336, while the sum is 41.

The square root of 21691778 is about 4657.4432900466. The cubic root of 21691778 is about 278.8892131750.

The spelling of 21691778 in words is "twenty-one million, six hundred ninety-one thousand, seven hundred seventy-eight".