216021521 has 2 divisors, whose sum is σ = 216021522. Its totient is φ = 216021520.

The previous prime is 216021517. The next prime is 216021569. The reversal of 216021521 is 125120612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 214212496 + 1809025 = 14636^2 + 1345^2 .

It is a cyclic number.

It is not a de Polignac number, because 216021521 - 2² = 216021517 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 216021493 and 216021502.

It is not a weakly prime, because it can be changed into another prime (216021511) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108010760 + 108010761.

It is an arithmetic number, because the mean of its divisors is an integer number (108010761).

Almost surely, 2^216021521 is an apocalyptic number.

It is an amenable number.

216021521 is a deficient number, since it is larger than the sum of its proper divisors (1).

216021521 is an equidigital number, since it uses as much as digits as its factorization.

216021521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 240, while the sum is 20.

The square root of 216021521 is about 14697.6705977512. The cubic root of 216021521 is about 600.0199261901.

Subtracting from 216021521 its reverse (125120612), we obtain a palindrome (90900909).

The spelling of 216021521 in words is "two hundred sixteen million, twenty-one thousand, five hundred twenty-one".