261905290505 has 8 divisors (see below), whose sum is σ = 322780574472. Its totient is φ = 203861415168.

The previous prime is 261905290501. The next prime is 261905290541. The reversal of 261905290505 is 505092509162.

It can be written as a sum of positive squares in 4 ways, for example, as 148301239801 + 113604050704 = 385099^2 + 337052^2 .

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 261905290505 - 2² = 261905290501 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (261905290501) 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, 707851952 + ... + 707852321.

It is an arithmetic number, because the mean of its divisors is an integer number (40347571809).

Almost surely, 2^261905290505 is an apocalyptic number.

It is an amenable number.

261905290505 is a deficient number, since it is larger than the sum of its proper divisors (60875283967).

261905290505 is a wasteful number, since it uses less digits than its factorization.

261905290505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1415704315.

The product of its (nonzero) digits is 243000, while the sum is 44.

Adding to 261905290505 its reverse (505092509162), we get a palindrome (766997799667).

The spelling of 261905290505 in words is "two hundred sixty-one billion, nine hundred five million, two hundred ninety thousand, five hundred five".