161521531 has 4 divisors (see below), whose sum is σ = 161717200. Its totient is φ = 161325864.

The previous prime is 161521517. The next prime is 161521537. The reversal of 161521531 is 135125161.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 161521531 - 2⁵ = 161521499 is a prime.

It is a super-2 number, since 2×161521531² = 52178409953167922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 161521496 and 161521505.

It is not an unprimeable number, because it can be changed into a prime (161521537) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 96591 + ... + 98248.

It is an arithmetic number, because the mean of its divisors is an integer number (40429300).

Almost surely, 2^161521531 is an apocalyptic number.

161521531 is a deficient number, since it is larger than the sum of its proper divisors (195669).

161521531 is an equidigital number, since it uses as much as digits as its factorization.

161521531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 195668.

The product of its digits is 900, while the sum is 25.

The square root of 161521531 is about 12709.1121247710. The cubic root of 161521531 is about 544.5989597982.

Adding to 161521531 its reverse (135125161), we get a palindrome (296646692).

The spelling of 161521531 in words is "one hundred sixty-one million, five hundred twenty-one thousand, five hundred thirty-one".