261631 has 2 divisors, whose sum is σ = 261632. Its totient is φ = 261630.

The previous prime is 261619. The next prime is 261637. The reversal of 261631 is 136162.

261631 is nontrivially palindromic in base 4.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 261631 - 2¹¹ = 259583 is a prime.

It is a super-2 number, since 2×261631² = 136901560322, which contains 22 as substring.

It is a Chen prime.

261631 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 261599 and 261608.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261637) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130815 + 130816.

It is an arithmetic number, because the mean of its divisors is an integer number (130816).

2²⁶¹⁶³¹ is an apocalyptic number.

261631 is the 324-th centered pentagonal number.

261631 is a deficient number, since it is larger than the sum of its proper divisors (1).

261631 is an equidigital number, since it uses as much as digits as its factorization.

261631 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 216, while the sum is 19.

The square root of 261631 is about 511.4987781022. The cubic root of 261631 is about 63.9582246907.

Adding to 261631 its reverse (136162), we get a palindrome (397793).

The spelling of 261631 in words is "two hundred sixty-one thousand, six hundred thirty-one".