278991261 has 6 divisors (see below), whose sum is σ = 402987390. Its totient is φ = 185994168.

The previous prime is 278991257. The next prime is 278991263. The reversal of 278991261 is 162199872.

It can be written as a sum of positive squares in only one way, i.e., 276723225 + 2268036 = 16635^2 + 1506^2 .

It is not a de Polignac number, because 278991261 - 2² = 278991257 is a prime.

It is a super-2 number, since 2×278991261² = 155672247428740242, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (278991263) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 15499506 + ... + 15499523.

It is an arithmetic number, because the mean of its divisors is an integer number (67164565).

Almost surely, 2^278991261 is an apocalyptic number.

It is an amenable number.

278991261 is a deficient number, since it is larger than the sum of its proper divisors (123996129).

278991261 is a wasteful number, since it uses less digits than its factorization.

278991261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30999035 (or 30999032 counting only the distinct ones).

The product of its digits is 108864, while the sum is 45.

The square root of 278991261 is about 16703.0314913192. The cubic root of 278991261 is about 653.4266852296.

The spelling of 278991261 in words is "two hundred seventy-eight million, nine hundred ninety-one thousand, two hundred sixty-one".