261539165281 has 3 divisors (see below), whose sum is σ = 261539676691. Its totient is φ = 261538653872.

The previous prime is 261539165269. The next prime is 261539165297. The reversal of 261539165281 is 182561935162.

The square root of 261539165281 is 511409.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 211792323681 + 49746841600 = 460209^2 + 223040^2 .

It is not a de Polignac number, because 261539165281 - 2⁵ = 261539165249 is a prime.

It is a super-2 number, since 2×261539165281² (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 (261539165201) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 255705 + ... + 767113.

Almost surely, 2^261539165281 is an apocalyptic number.

261539165281 is the 511409-th square number.

261539165281 is the 255705-th centered octagonal number.

It is an amenable number.

261539165281 is a deficient number, since it is larger than the sum of its proper divisors (511410).

261539165281 is an frugal number, since it uses more digits than its factorization.

261539165281 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1022818 (or 511409 counting only the distinct ones).

The product of its digits is 777600, while the sum is 49.

Multiplying 261539165281 by its sum of digits (49), we get a square (12815419098769 = 3579863²).

The spelling of 261539165281 in words is "two hundred sixty-one billion, five hundred thirty-nine million, one hundred sixty-five thousand, two hundred eighty-one".