42561721 has 4 divisors (see below), whose sum is σ = 42582244. Its totient is φ = 42541200.

The previous prime is 42561719. The next prime is 42561733. The reversal of 42561721 is 12716524.

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 35271721 + 7290000 = 5939^2 + 2700^2 .

It is a cyclic number.

It is not a de Polignac number, because 42561721 - 2¹ = 42561719 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 42561721.

It is not an unprimeable number, because it can be changed into a prime (42561221) 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, 6750 + ... + 11431.

It is an arithmetic number, because the mean of its divisors is an integer number (10645561).

Almost surely, 2^42561721 is an apocalyptic number.

It is an amenable number.

42561721 is a deficient number, since it is larger than the sum of its proper divisors (20523).

42561721 is a wasteful number, since it uses less digits than its factorization.

42561721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20522.

The product of its digits is 3360, while the sum is 28.

The square root of 42561721 is about 6523.9344723870. The cubic root of 42561721 is about 349.1454554157.

The spelling of 42561721 in words is "forty-two million, five hundred sixty-one thousand, seven hundred twenty-one".