261531631 has 2 divisors, whose sum is σ = 261531632. Its totient is φ = 261531630.

The previous prime is 261531629. The next prime is 261531649. The reversal of 261531631 is 136135162.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 261531631 - 2¹ = 261531629 is a prime.

It is a super-2 number, since 2×261531631² = 136797588027040322, which contains 22 as substring.

Together with 261531629, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 261531631.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261531131) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130765815 + 130765816.

It is an arithmetic number, because the mean of its divisors is an integer number (130765816).

Almost surely, 2^261531631 is an apocalyptic number.

261531631 is a deficient number, since it is larger than the sum of its proper divisors (1).

261531631 is an equidigital number, since it uses as much as digits as its factorization.

261531631 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 28.

The square root of 261531631 is about 16171.9396177453. The cubic root of 261531631 is about 639.5012642809.

Adding to 261531631 its reverse (136135162), we get a palindrome (397666793).

The spelling of 261531631 in words is "two hundred sixty-one million, five hundred thirty-one thousand, six hundred thirty-one".