21155842 has 4 divisors (see below), whose sum is σ = 31733766. Its totient is φ = 10577920.

The previous prime is 21155839. The next prime is 21155843. The reversal of 21155842 is 24855112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 21150801 + 5041 = 4599^2 + 71^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21155842.

It is not an unprimeable number, because it can be changed into a prime (21155843) by changing a digit.

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 as a sum of consecutive naturals, namely, 5288959 + ... + 5288962.

Almost surely, 2^21155842 is an apocalyptic number.

21155842 is a deficient number, since it is larger than the sum of its proper divisors (10577924).

21155842 is a wasteful number, since it uses less digits than its factorization.

21155842 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10577923.

The product of its digits is 3200, while the sum is 28.

The square root of 21155842 is about 4599.5480212734. The cubic root of 21155842 is about 276.5732066056.

It can be divided in two parts, 211558 and 42, that added together give a square (211600 = 460²).

The spelling of 21155842 in words is "twenty-one million, one hundred fifty-five thousand, eight hundred forty-two".