261505681 has 2 divisors, whose sum is σ = 261505682. Its totient is φ = 261505680.

The previous prime is 261505609. The next prime is 261505687. The reversal of 261505681 is 186505162.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 138650625 + 122855056 = 11775^2 + 11084^2 .

It is a cyclic number.

It is not a de Polignac number, because 261505681 - 2¹⁹ = 260981393 is a prime.

It is a super-2 number, since 2×261505681² = 136770442390547522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (261505687) 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 as a sum of consecutive naturals, namely, 130752840 + 130752841.

It is an arithmetic number, because the mean of its divisors is an integer number (130752841).

Almost surely, 2^261505681 is an apocalyptic number.

It is an amenable number.

261505681 is a deficient number, since it is larger than the sum of its proper divisors (1).

261505681 is an equidigital number, since it uses as much as digits as its factorization.

261505681 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 14400, while the sum is 34.

The square root of 261505681 is about 16171.1372822075. The cubic root of 261505681 is about 639.4801124651.

The spelling of 261505681 in words is "two hundred sixty-one million, five hundred five thousand, six hundred eighty-one".