42009721 has 4 divisors (see below), whose sum is σ = 45241252. Its totient is φ = 38778192.

The previous prime is 42009713. The next prime is 42009727. The reversal of 42009721 is 12790024.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 5588496 + 36421225 = 2364^2 + 6035^2 .

It is a cyclic number.

It is not a de Polignac number, because 42009721 - 2³ = 42009713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (42009727) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1615746 + ... + 1615771.

It is an arithmetic number, because the mean of its divisors is an integer number (11310313).

Almost surely, 2^42009721 is an apocalyptic number.

It is an amenable number.

42009721 is a deficient number, since it is larger than the sum of its proper divisors (3231531).

42009721 is a wasteful number, since it uses less digits than its factorization.

42009721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3231530.

The product of its (nonzero) digits is 1008, while the sum is 25.

The square root of 42009721 is about 6481.4906464485. The cubic root of 42009721 is about 347.6294802413.

Adding to 42009721 its reverse (12790024), we get a palindrome (54799745).

The spelling of 42009721 in words is "forty-two million, nine thousand, seven hundred twenty-one".