261621 has 12 divisors (see below), whose sum is σ = 387660. Its totient is φ = 169920.

The previous prime is 261619. The next prime is 261631. The reversal of 261621 is 126162.

261621 = 59² + 60² + ... + 99².

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 22500 + 239121 = 150^2 + 489^2 .

It is not a de Polignac number, because 261621 - 2¹ = 261619 is a prime.

It is an Ulam number.

It is a junction number, because it is equal to n+sod(n) for n = 261594 and 261603.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261601) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 15 + ... + 723.

It is an arithmetic number, because the mean of its divisors is an integer number (32305).

2²⁶¹⁶²¹ is an apocalyptic number.

It is an amenable number.

261621 is a deficient number, since it is larger than the sum of its proper divisors (126039).

261621 is a wasteful number, since it uses less digits than its factorization.

261621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 756 (or 753 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 261621 is about 511.4890028143. The cubic root of 261621 is about 63.9574098148.

Adding to 261621 its reverse (126162), we get a palindrome (387783).

The spelling of 261621 in words is "two hundred sixty-one thousand, six hundred twenty-one".