261505643 has 4 divisors (see below), whose sum is σ = 298863600. Its totient is φ = 224147688.

The previous prime is 261505609. The next prime is 261505681. The reversal of 261505643 is 346505162.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 261505643 - 2¹⁶ = 261440107 is a prime.

It is not an unprimeable number, because it can be changed into a prime (261505043) 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, 18678968 + ... + 18678981.

It is an arithmetic number, because the mean of its divisors is an integer number (74715900).

Almost surely, 2^261505643 is an apocalyptic number.

261505643 is a deficient number, since it is larger than the sum of its proper divisors (37357957).

261505643 is an equidigital number, since it uses as much as digits as its factorization.

261505643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37357956.

The product of its (nonzero) digits is 21600, while the sum is 32.

The square root of 261505643 is about 16171.1361072746. The cubic root of 261505643 is about 639.4800814903.

The spelling of 261505643 in words is "two hundred sixty-one million, five hundred five thousand, six hundred forty-three".