216642521 has 2 divisors, whose sum is σ = 216642522. Its totient is φ = 216642520.

The previous prime is 216642487. The next prime is 216642523. The reversal of 216642521 is 125246612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 156750400 + 59892121 = 12520^2 + 7739^2 .

It is a cyclic number.

It is not a de Polignac number, because 216642521 - 2¹⁰ = 216641497 is a prime.

It is a Sophie Germain prime.

Together with 216642523, it forms a pair of twin primes.

It is a Chen prime.

It is a pancake number, because a pancake can be divided into 216642521 parts by 20815 straight cuts.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (216642523) 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 as a sum of consecutive naturals, namely, 108321260 + 108321261.

It is an arithmetic number, because the mean of its divisors is an integer number (108321261).

Almost surely, 2^216642521 is an apocalyptic number.

It is an amenable number.

216642521 is a deficient number, since it is larger than the sum of its proper divisors (1).

216642521 is an equidigital number, since it uses as much as digits as its factorization.

216642521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5760, while the sum is 29.

The square root of 216642521 is about 14718.7812335125. The cubic root of 216642521 is about 600.5943379282.

The spelling of 216642521 in words is "two hundred sixteen million, six hundred forty-two thousand, five hundred twenty-one".