21391966 has 16 divisors (see below), whose sum is σ = 33825600. Its totient is φ = 10130848.

The previous prime is 21391949. The next prime is 21391987. The reversal of 21391966 is 66919312.

It is a congruent number.

It is an unprimeable number.

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, 406 + ... + 6553.

It is an arithmetic number, because the mean of its divisors is an integer number (2114100).

Almost surely, 2^21391966 is an apocalyptic number.

21391966 is a deficient number, since it is larger than the sum of its proper divisors (12433634).

21391966 is a wasteful number, since it uses less digits than its factorization.

21391966 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7043.

The product of its digits is 17496, while the sum is 37.

The square root of 21391966 is about 4625.1449707009. The cubic root of 21391966 is about 277.5983624466.

The spelling of 21391966 in words is "twenty-one million, three hundred ninety-one thousand, nine hundred sixty-six".