21001842 has 20 divisors (see below), whose sum is σ = 47060046. Its totient is φ = 7000560.

The previous prime is 21001837. The next prime is 21001843. The reversal of 21001842 is 24810012.

It can be written as a sum of positive squares in only one way, i.e., 20331081 + 670761 = 4509^2 + 819^2 .

It is a Harshad number since it is a multiple of its sum of digits (18).

It is not an unprimeable number, because it can be changed into a prime (21001843) 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 9 ways as a sum of consecutive naturals, for example, 64659 + ... + 64982.

Almost surely, 2^21001842 is an apocalyptic number.

21001842 is an abundant number, since it is smaller than the sum of its proper divisors (26058204).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21001842 is a wasteful number, since it uses less digits than its factorization.

21001842 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 129655 (or 129646 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 18.

The square root of 21001842 is about 4582.7766692258. The cubic root of 21001842 is about 275.9004839711.

Adding to 21001842 its reverse (24810012), we get a palindrome (45811854).

The spelling of 21001842 in words is "twenty-one million, one thousand, eight hundred forty-two".