2561639 has 8 divisors (see below), whose sum is σ = 2686992. Its totient is φ = 2439360.

The previous prime is 2561633. The next prime is 2561651. The reversal of 2561639 is 9361652.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 2561639 - 2¹⁶ = 2496103 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2561633) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1037 + ... + 2489.

It is an arithmetic number, because the mean of its divisors is an integer number (335874).

2^2561639 is an apocalyptic number.

2561639 is a deficient number, since it is larger than the sum of its proper divisors (125353).

2561639 is a wasteful number, since it uses less digits than its factorization.

2561639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1537.

The product of its digits is 9720, while the sum is 32.

The square root of 2561639 is about 1600.5121055462. The cubic root of 2561639 is about 136.8272637828.

The spelling of 2561639 in words is "two million, five hundred sixty-one thousand, six hundred thirty-nine".