261819 has 8 divisors (see below), whose sum is σ = 387920. Its totient is φ = 174528.

The previous prime is 261799. The next prime is 261823. The reversal of 261819 is 918162.

It is not a de Polignac number, because 261819 - 2⁵ = 261787 is a prime.

It is a super-2 number, since 2×261819² = 137098377522, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 9697 = 261819 / (2 + 6 + 1 + 8 + 1 + 9).

It is a Duffinian number.

261819 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 261792 and 261801.

It is not an unprimeable number, because it can be changed into a prime (261619) 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, 4822 + ... + 4875.

It is an arithmetic number, because the mean of its divisors is an integer number (48490).

2²⁶¹⁸¹⁹ is an apocalyptic number.

261819 is a deficient number, since it is larger than the sum of its proper divisors (126101).

261819 is an equidigital number, since it uses as much as digits as its factorization.

261819 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9706 (or 9700 counting only the distinct ones).

The product of its digits is 864, while the sum is 27.

The square root of 261819 is about 511.6825187555. The cubic root of 261819 is about 63.9735404947.

The spelling of 261819 in words is "two hundred sixty-one thousand, eight hundred nineteen".