216556621 has 2 divisors, whose sum is σ = 216556622. Its totient is φ = 216556620.

The previous prime is 216556583. The next prime is 216556651. The reversal of 216556621 is 126655612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 205922500 + 10634121 = 14350^2 + 3261^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-216556621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216556651) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108278310 + 108278311.

It is an arithmetic number, because the mean of its divisors is an integer number (108278311).

Almost surely, 2^216556621 is an apocalyptic number.

It is an amenable number.

216556621 is a deficient number, since it is larger than the sum of its proper divisors (1).

216556621 is an equidigital number, since it uses as much as digits as its factorization.

216556621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 21600, while the sum is 34.

The square root of 216556621 is about 14715.8629036832. The cubic root of 216556621 is about 600.5149477364.

The spelling of 216556621 in words is "two hundred sixteen million, five hundred fifty-six thousand, six hundred twenty-one".