21090042 has 12 divisors (see below), whose sum is σ = 45695130. Its totient is φ = 7030008.

The previous prime is 21090007. The next prime is 21090061. The reversal of 21090042 is 24009012.

It can be written as a sum of positive squares in only one way, i.e., 15515721 + 5574321 = 3939^2 + 2361^2 .

It is a Harshad number since it is a multiple of its sum of digits (18), and also a Moran number because the ratio is a prime number: 1171669 = 21090042 / (2 + 1 + 0 + 9 + 0 + 0 + 4 + 2).

It is a junction number, because it is equal to n+sod(n) for n = 21089997 and 21090024.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 585817 + ... + 585852.

Almost surely, 2^21090042 is an apocalyptic number.

21090042 is an abundant number, since it is smaller than the sum of its proper divisors (24605088).

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

21090042 is a wasteful number, since it uses less digits than its factorization.

21090042 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1171677 (or 1171674 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21090042 is about 4592.3895740671. The cubic root of 21090042 is about 276.2861713588.

Adding to 21090042 its reverse (24009012), we get a palindrome (45099054).

The spelling of 21090042 in words is "twenty-one million, ninety thousand, forty-two".