21000042 has 24 divisors (see below), whose sum is σ = 52000416. Its totient is φ = 5999976.

The previous prime is 21000041. The next prime is 21000059. The reversal of 21000042 is 24000012.

It is a super-3 number, since 3×21000042³ (a number of 23 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a junction number, because it is equal to n+sod(n) for n = 20999988 and 21000033.

It is not an unprimeable number, because it can be changed into a prime (21000041) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 83208 + ... + 83459.

It is an arithmetic number, because the mean of its divisors is an integer number (2166684).

Almost surely, 2^21000042 is an apocalyptic number.

21000042 is an abundant number, since it is smaller than the sum of its proper divisors (31000374).

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

21000042 is a wasteful number, since it uses less digits than its factorization.

21000042 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 166682 (or 166679 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 9.

The square root of 21000042 is about 4582.5802775292. The cubic root of 21000042 is about 275.8926015663.

Adding to 21000042 its reverse (24000012), we get a palindrome (45000054).

The spelling of 21000042 in words is "twenty-one million, forty-two", and thus it is an aban number and an uban number.