261821505 has 64 divisors (see below), whose sum is σ = 499654656. Its totient is φ = 115584000.

The previous prime is 261821503. The next prime is 261821513. The reversal of 261821505 is 505128162.

It is not a de Polignac number, because 261821505 - 2¹ = 261821503 is a prime.

It is not an unprimeable number, because it can be changed into a prime (261821503) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 85450 + ... + 88460.

It is an arithmetic number, because the mean of its divisors is an integer number (7807104).

Almost surely, 2^261821505 is an apocalyptic number.

It is an amenable number.

261821505 is a deficient number, since it is larger than the sum of its proper divisors (237833151).

261821505 is a wasteful number, since it uses less digits than its factorization.

261821505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3078.

The product of its (nonzero) digits is 4800, while the sum is 30.

The square root of 261821505 is about 16180.8993878585. The cubic root of 261821505 is about 639.7374452009.

Adding to 261821505 its reverse (505128162), we get a palindrome (766949667).

The spelling of 261821505 in words is "two hundred sixty-one million, eight hundred twenty-one thousand, five hundred five".