161657251 has 4 divisors (see below), whose sum is σ = 184751152. Its totient is φ = 138563352.

The previous prime is 161657239. The next prime is 161657291. The reversal of 161657251 is 152756161.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 152756161 = 353 ⋅432737.

It is a cyclic number.

It is not a de Polignac number, because 161657251 - 2²⁷ = 27439523 is a prime.

It is a super-2 number, since 2×161657251² = 52266133601754002, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (161657201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11546940 + ... + 11546953.

It is an arithmetic number, because the mean of its divisors is an integer number (46187788).

Almost surely, 2^161657251 is an apocalyptic number.

161657251 is a deficient number, since it is larger than the sum of its proper divisors (23093901).

161657251 is an equidigital number, since it uses as much as digits as its factorization.

161657251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23093900.

The product of its digits is 12600, while the sum is 34.

The square root of 161657251 is about 12714.4504796708. The cubic root of 161657251 is about 544.7514519107.

The spelling of 161657251 in words is "one hundred sixty-one million, six hundred fifty-seven thousand, two hundred fifty-one".