161720656521 has 16 divisors (see below), whose sum is σ = 217648204800. Its totient is φ = 106807695120.

The previous prime is 161720656459. The next prime is 161720656529. The reversal of 161720656521 is 125656027161.

It is not a de Polignac number, because 161720656521 - 2⁷ = 161720656393 is a prime.

It is not an unprimeable number, because it can be changed into a prime (161720656529) 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, 379621 + ... + 683778.

It is an arithmetic number, because the mean of its divisors is an integer number (13603012800).

Almost surely, 2^161720656521 is an apocalyptic number.

It is an amenable number.

161720656521 is a deficient number, since it is larger than the sum of its proper divisors (55927548279).

161720656521 is a wasteful number, since it uses less digits than its factorization.

161720656521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1063876.

The product of its (nonzero) digits is 151200, while the sum is 42.

The spelling of 161720656521 in words is "one hundred sixty-one billion, seven hundred twenty million, six hundred fifty-six thousand, five hundred twenty-one".