21181994 has 8 divisors (see below), whose sum is σ = 32548068. Its totient is φ = 10332640.

The previous prime is 21181961. The next prime is 21181997. The reversal of 21181994 is 49918112.

It can be written as a sum of positive squares in 2 ways, for example, as 19035769 + 2146225 = 4363^2 + 1465^2 .

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

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21181997) by changing a digit.

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, 129077 + ... + 129240.

Almost surely, 2^21181994 is an apocalyptic number.

21181994 is a deficient number, since it is larger than the sum of its proper divisors (11366074).

21181994 is a wasteful number, since it uses less digits than its factorization.

21181994 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 258360.

The product of its digits is 5184, while the sum is 35.

The square root of 21181994 is about 4602.3900312772. The cubic root of 21181994 is about 276.6871225662.

The spelling of 21181994 in words is "twenty-one million, one hundred eighty-one thousand, nine hundred ninety-four".