21309442 has 16 divisors (see below), whose sum is σ = 39851712. Its totient is φ = 8302320.

The previous prime is 21309437. The next prime is 21309487. The reversal of 21309442 is 24490312.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 69033 + ... + 69340.

It is an arithmetic number, because the mean of its divisors is an integer number (2490732).

Almost surely, 2^21309442 is an apocalyptic number.

21309442 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

21309442 is a deficient number, since it is larger than the sum of its proper divisors (18542270).

21309442 is a wasteful number, since it uses less digits than its factorization.

21309442 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 138393.

The product of its (nonzero) digits is 1728, while the sum is 25.

The square root of 21309442 is about 4616.2151163047. The cubic root of 21309442 is about 277.2409377837.

Adding to 21309442 its reverse (24490312), we get a palindrome (45799754).

The spelling of 21309442 in words is "twenty-one million, three hundred nine thousand, four hundred forty-two".