261820 has 48 divisors (see below), whose sum is σ = 635040. Its totient is φ = 89856.

The previous prime is 261799. The next prime is 261823. The reversal of 261820 is 28162.

It is a happy number.

261820 is nontrivially palindromic in base 14.

It is a Harshad number since it is a multiple of its sum of digits (19).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261823) by changing a digit.

261820 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4914 + ... + 4966.

It is an arithmetic number, because the mean of its divisors is an integer number (13230).

2²⁶¹⁸²⁰ is an apocalyptic number.

261820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (317520).

261820 is an abundant number, since it is smaller than the sum of its proper divisors (373220).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

261820 is a wasteful number, since it uses less digits than its factorization.

261820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 94 (or 92 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 19.

The square root of 261820 is about 511.6834959230. The cubic root of 261820 is about 63.9736219421.

Adding to 261820 its reverse (28162), we get a palindrome (289982).

It can be divided in two parts, 261 and 820, that added together give a triangular number (1081 = T₄₆).

The spelling of 261820 in words is "two hundred sixty-one thousand, eight hundred twenty".