21991942 has 32 divisors (see below), whose sum is σ = 38697984. Its totient is φ = 9180000.

The previous prime is 21991939. The next prime is 21991943. The reversal of 21991942 is 24919912.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21991943) 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 15 ways as a sum of consecutive naturals, for example, 145567 + ... + 145717.

It is an arithmetic number, because the mean of its divisors is an integer number (1209312).

Almost surely, 2^21991942 is an apocalyptic number.

21991942 is a deficient number, since it is larger than the sum of its proper divisors (16706042).

21991942 is a wasteful number, since it uses less digits than its factorization.

21991942 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 364.

The product of its digits is 11664, while the sum is 37.

The square root of 21991942 is about 4689.5566954671. The cubic root of 21991942 is about 280.1697185350.

It can be divided in two parts, 219919 and 42, that added together give a square (219961 = 469²).

The spelling of 21991942 in words is "twenty-one million, nine hundred ninety-one thousand, nine hundred forty-two".