21391994 has 24 divisors (see below), whose sum is σ = 35574588. Its totient is φ = 9590400.

The previous prime is 21391987. The next prime is 21391999. The reversal of 21391994 is 49919312.

It can be written as a sum of positive squares in 6 ways, for example, as 19035769 + 2356225 = 4363^2 + 1535^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21391999) 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 11 ways as a sum of consecutive naturals, for example, 35294 + ... + 35894.

Almost surely, 2^21391994 is an apocalyptic number.

21391994 is a deficient number, since it is larger than the sum of its proper divisors (14182594).

21391994 is a wasteful number, since it uses less digits than its factorization.

21391994 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 690 (or 653 counting only the distinct ones).

The product of its digits is 17496, while the sum is 38.

The square root of 21391994 is about 4625.1479976321. The cubic root of 21391994 is about 277.5984835630.

The spelling of 21391994 in words is "twenty-one million, three hundred ninety-one thousand, nine hundred ninety-four".