42042821 has 2 divisors, whose sum is σ = 42042822. Its totient is φ = 42042820.

The previous prime is 42042811. The next prime is 42042823. The reversal of 42042821 is 12824024.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 34281025 + 7761796 = 5855^2 + 2786^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-42042821 is a prime.

It is a Sophie Germain prime.

Together with 42042823, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (42042823) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 21021410 + 21021411.

It is an arithmetic number, because the mean of its divisors is an integer number (21021411).

Almost surely, 2^42042821 is an apocalyptic number.

It is an amenable number.

42042821 is a deficient number, since it is larger than the sum of its proper divisors (1).

42042821 is an equidigital number, since it uses as much as digits as its factorization.

42042821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1024, while the sum is 23.

The square root of 42042821 is about 6484.0435686383. The cubic root of 42042821 is about 347.7207568538.

Adding to 42042821 its reverse (12824024), we get a palindrome (54866845).

The spelling of 42042821 in words is "forty-two million, forty-two thousand, eight hundred twenty-one".