21020842 has 4 divisors (see below), whose sum is σ = 31531266. Its totient is φ = 10510420.

The previous prime is 21020837. The next prime is 21020843. The reversal of 21020842 is 24802012.

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., 13242321 + 7778521 = 3639^2 + 2789^2 .

It is not an unprimeable number, because it can be changed into a prime (21020843) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5255209 + ... + 5255212.

Almost surely, 2^21020842 is an apocalyptic number.

21020842 is a deficient number, since it is larger than the sum of its proper divisors (10510424).

21020842 is a wasteful number, since it uses less digits than its factorization.

21020842 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10510423.

The product of its (nonzero) digits is 256, while the sum is 19.

The square root of 21020842 is about 4584.8491796350. The cubic root of 21020842 is about 275.9836596781.

Adding to 21020842 its reverse (24802012), we get a palindrome (45822854).

The spelling of 21020842 in words is "twenty-one million, twenty thousand, eight hundred forty-two".