2561721 has 16 divisors (see below), whose sum is σ = 3568320. Its totient is φ = 1633280.

The previous prime is 2561683. The next prime is 2561723. The reversal of 2561721 is 1271652.

It is a cyclic number.

It is not a de Polignac number, because 2561721 - 2⁷ = 2561593 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 2561691 and 2561700.

It is not an unprimeable number, because it can be changed into a prime (2561723) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7081 + ... + 7433.

It is an arithmetic number, because the mean of its divisors is an integer number (223020).

2^2561721 is an apocalyptic number.

It is an amenable number.

2561721 is a deficient number, since it is larger than the sum of its proper divisors (1006599).

2561721 is a wasteful number, since it uses less digits than its factorization.

2561721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 456.

The product of its digits is 840, while the sum is 24.

The square root of 2561721 is about 1600.5377221422. The cubic root of 2561721 is about 136.8287237486.

It can be divided in two parts, 2561 and 721, that multiplied together give a palindrome (1846481).

The spelling of 2561721 in words is "two million, five hundred sixty-one thousand, seven hundred twenty-one".