261990 has 48 divisors (see below), whose sum is σ = 707616. Its totient is φ = 67200.

The previous prime is 261983. The next prime is 262007. The reversal of 261990 is 99162.

It is a happy number.

It is an Ulam number.

It is a congruent number.

It is an unprimeable number.

261990 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 23 ways as a sum of consecutive naturals, for example, 3655 + ... + 3725.

It is an arithmetic number, because the mean of its divisors is an integer number (14742).

2²⁶¹⁹⁹⁰ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (353808).

261990 is an abundant number, since it is smaller than the sum of its proper divisors (445626).

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

261990 is a wasteful number, since it uses less digits than its factorization.

261990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 125 (or 122 counting only the distinct ones).

The product of its (nonzero) digits is 972, while the sum is 27.

The square root of 261990 is about 511.8495872813. The cubic root of 261990 is about 63.9874649930.

It can be divided in two parts, 26 and 1990, that added together give a triangular number (2016 = T₆₃).

The spelling of 261990 in words is "two hundred sixty-one thousand, nine hundred ninety".