261157991 has 8 divisors (see below), whose sum is σ = 267019200. Its totient is φ = 255309568.

The previous prime is 261157979. The next prime is 261157999. The reversal of 261157991 is 199751162.

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 261157991 - 2¹⁰ = 261156967 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261157999) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 46655 + ... + 51951.

It is an arithmetic number, because the mean of its divisors is an integer number (33377400).

Almost surely, 2^261157991 is an apocalyptic number.

261157991 is a deficient number, since it is larger than the sum of its proper divisors (5861209).

261157991 is a wasteful number, since it uses less digits than its factorization.

261157991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6393.

The product of its digits is 34020, while the sum is 41.

The square root of 261157991 is about 16160.3833803533. The cubic root of 261157991 is about 639.1965756645.

The spelling of 261157991 in words is "two hundred sixty-one million, one hundred fifty-seven thousand, nine hundred ninety-one".