216721557 has 18 divisors (see below), whose sum is σ = 337370306. Its totient is φ = 133269120.

The previous prime is 216721529. The next prime is 216721567. The reversal of 216721557 is 755127612.

216721557 is a `hidden beast` number, since 21 + 67 + 21 + 557 = 666.

It can be written as a sum of positive squares in 3 ways, for example, as 5716881 + 211004676 = 2391^2 + 14526^2 .

It is not a de Polignac number, because 216721557 - 2⁶ = 216721493 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216721517) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 158557 + ... + 159917.

Almost surely, 2^216721557 is an apocalyptic number.

It is an amenable number.

216721557 is a deficient number, since it is larger than the sum of its proper divisors (120648749).

216721557 is an equidigital number, since it uses as much as digits as its factorization.

216721557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2741 (or 1377 counting only the distinct ones).

The product of its digits is 29400, while the sum is 36.

The square root of 216721557 is about 14721.4658577195. The cubic root of 216721557 is about 600.6673657630.

The spelling of 216721557 in words is "two hundred sixteen million, seven hundred twenty-one thousand, five hundred fifty-seven".