261636251 has 4 divisors (see below), whose sum is σ = 275406600. Its totient is φ = 247865904.

The previous prime is 261636233. The next prime is 261636253. The reversal of 261636251 is 152636162.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261636251 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261636253) 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 in 3 ways as a sum of consecutive naturals, for example, 6885146 + ... + 6885183.

It is an arithmetic number, because the mean of its divisors is an integer number (68851650).

Almost surely, 2^261636251 is an apocalyptic number.

261636251 is a deficient number, since it is larger than the sum of its proper divisors (13770349).

261636251 is a wasteful number, since it uses less digits than its factorization.

261636251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13770348.

The product of its digits is 12960, while the sum is 32.

The square root of 261636251 is about 16175.1739094206. The cubic root of 261636251 is about 639.5865257370.

The spelling of 261636251 in words is "two hundred sixty-one million, six hundred thirty-six thousand, two hundred fifty-one".