2491561 has 4 divisors (see below), whose sum is σ = 2494800. Its totient is φ = 2488324.

The previous prime is 2491553. The next prime is 2491589. The reversal of 2491561 is 1651942.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1651942 = 2 ⋅825971.

It is a cyclic number.

It is not a de Polignac number, because 2491561 - 2³ = 2491553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2491661) 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, 270 + ... + 2248.

It is an arithmetic number, because the mean of its divisors is an integer number (623700).

2^2491561 is an apocalyptic number.

It is an amenable number.

2491561 is a deficient number, since it is larger than the sum of its proper divisors (3239).

2491561 is a wasteful number, since it uses less digits than its factorization.

2491561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3238.

The product of its digits is 2160, while the sum is 28.

The square root of 2491561 is about 1578.4679280872. The cubic root of 2491561 is about 135.5679955388.

It can be divided in two parts, 24915 and 61, that added together give a triangular number (24976 = T₂₂₃).

The spelling of 2491561 in words is "two million, four hundred ninety-one thousand, five hundred sixty-one".