261665651536623 has 24 divisors (see below), whose sum is σ = 378052330331520. Its totient is φ = 174401846622720.

The previous prime is 261665651536609. The next prime is 261665651536633. The reversal of 261665651536623 is 326635156566162.

It is a happy number.

261665651536623 is a `hidden beast` number, since 2 + 6 + 1 + 6 + 6 + 56 + 515 + 3 + 6 + 62 + 3 = 666.

It is not a de Polignac number, because 261665651536623 - 2⁵ = 261665651536591 is a prime.

It is a super-2 number, since 2×261665651536623² (a number of 30 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261665651536603) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (31) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 2059760715 + ... + 2059887747.

It is an arithmetic number, because the mean of its divisors is an integer number (15752180430480).

Almost surely, 2^{261665651536623} is an apocalyptic number.

261665651536623 is a deficient number, since it is larger than the sum of its proper divisors (116386678794897).

261665651536623 is a wasteful number, since it uses less digits than its factorization.

261665651536623 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 180239 (or 180236 counting only the distinct ones).

The product of its digits is 209952000, while the sum is 63.

The spelling of 261665651536623 in words is "two hundred sixty-one trillion, six hundred sixty-five billion, six hundred fifty-one million, five hundred thirty-six thousand, six hundred twenty-three".