261665651514581 has 2 divisors, whose sum is σ = 261665651514582. Its totient is φ = 261665651514580.

The previous prime is 261665651514569. The next prime is 261665651514643. The reversal of 261665651514581 is 185415156566162.

It is an a-pointer prime, because the next prime (261665651514643) can be obtained adding 261665651514581 to its sum of digits (62).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 175414793580625 + 86250857933956 = 13244425^2 + 9287134^2 .

It is a cyclic number.

It is not a de Polignac number, because 261665651514581 - 2⁶ = 261665651514517 is a prime.

It is a super-2 number, since 2×261665651514581² (a number of 30 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261665651714581) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (29) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130832825757290 + 130832825757291.

It is an arithmetic number, because the mean of its divisors is an integer number (130832825757291).

Almost surely, 2^{261665651514581} is an apocalyptic number.

It is an amenable number.

261665651514581 is a deficient number, since it is larger than the sum of its proper divisors (1).

261665651514581 is an equidigital number, since it uses as much as digits as its factorization.

261665651514581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 51840000, while the sum is 62.

The spelling of 261665651514581 in words is "two hundred sixty-one trillion, six hundred sixty-five billion, six hundred fifty-one million, five hundred fourteen thousand, five hundred eighty-one".