261487784161 has 4 divisors (see below), whose sum is σ = 261489240324. Its totient is φ = 261486328000.

The previous prime is 261487784113. The next prime is 261487784189. The reversal of 261487784161 is 161487784162.

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

It can be written as a sum of positive squares in 2 ways, for example, as 248387608225 + 13100175936 = 498385^2 + 114456^2 .

It is a cyclic number.

It is not a de Polignac number, because 261487784161 - 2⁹ = 261487783649 is a prime.

It is a super-2 number, since 2×261487784161² (a number of 24 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261487784101) 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, 413380 + ... + 832981.

It is an arithmetic number, because the mean of its divisors is an integer number (65372310081).

Almost surely, 2^261487784161 is an apocalyptic number.

It is an amenable number.

261487784161 is a deficient number, since it is larger than the sum of its proper divisors (1456163).

261487784161 is a wasteful number, since it uses less digits than its factorization.

261487784161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1456162.

The product of its digits is 3612672, while the sum is 55.

Subtracting from 261487784161 its reverse (161487784162), we obtain a palindrome (99999999999).

The spelling of 261487784161 in words is "two hundred sixty-one billion, four hundred eighty-seven million, seven hundred eighty-four thousand, one hundred sixty-one".