161720656520 has 32 divisors (see below), whose sum is σ = 364511021400. Its totient is φ = 64574565888.

The previous prime is 161720656459. The next prime is 161720656529. The reversal of 161720656520 is 25656027161.

It can be written as a sum of positive squares in 4 ways, for example, as 79685385796 + 82035270724 = 282286^2 + 286418^2 .

It is not an unprimeable number, because it can be changed into a prime (161720656529) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3529979 + ... + 3575498.

Almost surely, 2^161720656520 is an apocalyptic number.

161720656520 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

161720656520 is an abundant number, since it is smaller than the sum of its proper divisors (202790364880).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

161720656520 is a wasteful number, since it uses less digits than its factorization.

161720656520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7106057 (or 7106053 counting only the distinct ones).

The product of its (nonzero) digits is 151200, while the sum is 41.

The spelling of 161720656520 in words is "one hundred sixty-one billion, seven hundred twenty million, six hundred fifty-six thousand, five hundred twenty".