161865405625 has 225 divisors, whose sum is σ = 273156534585. Its totient is φ = 95592420000.

The previous prime is 161865405601. The next prime is 161865405649. The reversal of 161865405625 is 526504568161.

The square root of 161865405625 is 402325.

It is a perfect power (a square), and thus also a powerful number.

It is an interprime number because it is at equal distance from previous prime (161865405601) and next prime (161865405649).

It can be written as a sum of positive squares in 2 ways, for example, as 12690247801 + 149175157824 = 112651^2 + 386232^2 .

It is not a de Polignac number, because 161865405625 - 2⁵ = 161865405593 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (49).

It is an unprimeable number.

It is a polite number, since it can be written in 224 ways as a sum of consecutive naturals, for example, 8519231866 + ... + 8519231884.

Almost surely, 2^161865405625 is an apocalyptic number.

161865405625 is the 402325-th square number.

161865405625 is the 201163-rd centered octagonal number.

It is an amenable number.

161865405625 is a deficient number, since it is larger than the sum of its proper divisors (111291128960).

161865405625 is an frugal number, since it uses more digits than its factorization.

161865405625 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 116 (or 42 counting only the distinct ones).

The product of its (nonzero) digits is 1728000, while the sum is 49.

Multiplying 161865405625 by its sum of digits (49), we get a square (7931404875625 = 2816275²).

161865405625 divided by its sum of digits (49) gives a square (3303375625 = 57475²).

The spelling of 161865405625 in words is "one hundred sixty-one billion, eight hundred sixty-five million, four hundred five thousand, six hundred twenty-five".