131605721 has 16 divisors (see below), whose sum is σ = 151061904. Its totient is φ = 113577984.

The previous prime is 131605709. The next prime is 131605739. The reversal of 131605721 is 127506131.

It can be written as a sum of positive squares in 8 ways, for example, as 13579225 + 118026496 = 3685^2 + 10864^2 .

It is not a de Polignac number, because 131605721 - 2²⁶ = 64496857 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (131605321) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 32801 + ... + 36593.

It is an arithmetic number, because the mean of its divisors is an integer number (9441369).

Almost surely, 2^131605721 is an apocalyptic number.

It is an amenable number.

131605721 is a deficient number, since it is larger than the sum of its proper divisors (19456183).

131605721 is a wasteful number, since it uses less digits than its factorization.

131605721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3980.

The product of its (nonzero) digits is 1260, while the sum is 26.

The square root of 131605721 is about 11471.9536697112. The cubic root of 131605721 is about 508.6568798490.

It can be divided in two parts, 13160 and 5721, that added together give a palindrome (18881).

The spelling of 131605721 in words is "one hundred thirty-one million, six hundred five thousand, seven hundred twenty-one".