61578721 has 4 divisors (see below), whose sum is σ = 61607700. Its totient is φ = 61549744.

The previous prime is 61578701. The next prime is 61578733. The reversal of 61578721 is 12787516.

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 57168721 + 4410000 = 7561^2 + 2100^2 .

It is a cyclic number.

It is not a de Polignac number, because 61578721 - 2⁷ = 61578593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (61578701) 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, 11026 + ... + 15643.

It is an arithmetic number, because the mean of its divisors is an integer number (15401925).

Almost surely, 2^61578721 is an apocalyptic number.

It is an amenable number.

61578721 is a deficient number, since it is larger than the sum of its proper divisors (28979).

61578721 is a wasteful number, since it uses less digits than its factorization.

61578721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28978.

The product of its digits is 23520, while the sum is 37.

The square root of 61578721 is about 7847.2110332270. The cubic root of 61578721 is about 394.8906838445.

It can be divided in two parts, 6157 and 8721, that added together give a triangular number (14878 = T₁₇₂).

The spelling of 61578721 in words is "sixty-one million, five hundred seventy-eight thousand, seven hundred twenty-one".