16520217961 has 9 divisors (see below), whose sum is σ = 17890566231. Its totient is φ = 15247889592.

The previous prime is 16520217943. The next prime is 16520217991. The reversal of 16520217961 is 16971202561.

The square root of 16520217961 is 128531.

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

It can be written as a sum of positive squares in only one way, i.e., 2443819225 + 14076398736 = 49435^2 + 118644^2 .

It is not a de Polignac number, because 16520217961 - 2¹⁵ = 16520185193 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16520217991) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 1665960 + ... + 1675846.

Almost surely, 2^16520217961 is an apocalyptic number.

16520217961 is the 128531-st square number.

16520217961 is the 64266-th centered octagonal number.

It is an amenable number.

16520217961 is a deficient number, since it is larger than the sum of its proper divisors (1370348270).

16520217961 is an frugal number, since it uses more digits than its factorization.

16520217961 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19800 (or 9900 counting only the distinct ones).

The product of its (nonzero) digits is 45360, while the sum is 40.

The spelling of 16520217961 in words is "sixteen billion, five hundred twenty million, two hundred seventeen thousand, nine hundred sixty-one".