261515551 has 8 divisors (see below), whose sum is σ = 291924864. Its totient is φ = 232212120.

The previous prime is 261515549. The next prime is 261515581. The reversal of 261515551 is 155515162.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 261515551 - 2¹ = 261515549 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261515531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 275971 + ... + 276916.

It is an arithmetic number, because the mean of its divisors is an integer number (36490608).

Almost surely, 2^261515551 is an apocalyptic number.

261515551 is a deficient number, since it is larger than the sum of its proper divisors (30409313).

261515551 is a wasteful number, since it uses less digits than its factorization.

261515551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 552941.

The product of its digits is 7500, while the sum is 31.

The square root of 261515551 is about 16171.4424526695. The cubic root of 261515551 is about 639.4881576559.

The spelling of 261515551 in words is "two hundred sixty-one million, five hundred fifteen thousand, five hundred fifty-one".